Updated on the character. The eidolon build, as far as I'm aware, cannot be replicated by a caster.
For the Summoner
The Gyoji
Half-Elf Summoner 15, 20pb
HD 15d8+60 (131hp)
Ability Scores: 7, 12, 18, 10, 10, 29
BAB +11
AC 11 (+1 Dex)
Saves +5/+5/+9
Feats: Extra Evolution x4, Improved Share Spells (Share w/both, half duration), Resilient Eidolon (Stays for 15 rounds if owner killed), Spell Focus (Conjuration), Augment Summoning
Skills: Spellcraft +18, Use Magic Device +27
Spells/Day (8/7/7/6/5; DC 19+SL)
Spells Known (6/6/6/5/4/4)
1st - Enlarge Person, Mage Armor, Reduce Person
2nd - See Invisibility, Summon Eidolon
3rd - Dimensional Anchor, Charm Monster, Invisibility (Greater), Magic Circle Against Evil
4th - Evolution Surge (Greater), Magic Jar, Baleful Polymorph
5th - Planar Binding, True Seeing
Equipment (240k): Cloak of Resistance +5 (25k*), Permanent Magic Fang +5 (8k*), Headband of Alluring Charisma +6 (36k), Belt of Giant Strength +6 (36k), Normal Metamagic Rod of Extend (11k), Eyes of the Eagle (2.5k*), Amulet of Natural Armor +2 (8k), Ring of Protection +5 (50k*), Ring of Invisibility (20k*), Magically Reinforced Steel Coffin (inner lock), Wand of Silent Image (.75k), Bribe Money (42.25k)
Adventuring Assumptions: Up to a week prior to any adventuring, perform an extended binding on four separate monsters (glabrezu, shadow demon, X, X) and use an extended charm monster or two on some easily controlled brute; which can be done over the span of like one or two days. I am presuming that you only charm stuff that doesn't give XP under 3E rules, so CR 7 monsters will be your body-fodder (invisible stalker presumed at this point). The day prior, cast an extended mage armor on your eidolon & an extended magic jar, then enter the body of the invisible stalker you charmed. Now you're ready to go forth and slaughter everything.
For the Eidolon

Andre the literal Giant
TN Huge Outsider (
enlarge person presumed below)
Speed: 30' fly (perfect)
HD 12d10+60 (126hp)
Init +6,
Senses Perception +20, Darkvision 60'
AC 44 (+27 natural, +4 armor, +2 Dex, -4 size, +5 Deflection)
* CMB +37 (+45 grapple)
* CMD 47 (49 grapple)
Attacks: 2 claws +29 (2d6+21)
Saves Fort +18, Ref +11, Will +13 (+4 vs enchantment, Improved Evasion)
Abilities: Str 42, Dex 14, Con 21, Int 7, Wis 10, Cha 11
Skills: Perception +20, Use Magic Device +15, Stealth +5, Diplomacy +15
Feats: Imp Unarmed Strike, Improved Grapple, Greater Grapple, Lunge, Improved Initiative, Rapid Grappler
Evolutions: Huge, Perfect Flight, Spell Resistance, Grab, Improved Natural Armor x3, Fast Heal 1
And now, let's get ready to rrrumble with some SGT goodness.
Marut: There's a conversion of it
here. As it turns out, it's not very good at stealthing up to anything, but it has awesome stealth-detection powers with that
true seeing and +26 Perception. On the whole, both parties will recognize the other, but it's initiative is appreciably lower, it needs to a natural 20 to get past the eidolon's SR, & a natural 17 to hit with its fists. The eidolon, however, is going to auto-grapple/pin, and the concentration DC is solidly in the realm of laughing while it's curb-stomped to death.
Conugon: Very similar principle to the marut, except the lack of
true seeing gives us the element of surprise and the glabrezu's own sight gives us an excellent forward element. Impossible to evade the grapple, slowly beaten into a pulp in which it will take weeks to regenerate into consciousness from, and its +1 unholy spiked chain sold for money.
Pair of Glabrezus: Really? We've already got one in our own party, potentially three, and that's before we even bring in Andre the Giant.
Mature Black Dragon: Switching out the color due to CR changes to Pathfinder. The only thing that can even touch Andre is the dragon's breath weapon, which is doing ~12 damage on average (25 avg on a failed save), which is plenty of time for everyone to continue the curbstomp.
Score of Dire Bears: They have 5' reach, and Andre has 15' reach while flying without buffs. This is harvesting.
Cloud Giant Keg Party: None of their attacks are hitting unless they get a natural 20 (same goes for grappling escape), they can't see us coming, and don't even have darkvision. We're going goddamn Batman on these guys. The shadow demon can take them by himself.
Mansion of Succubi Bunnies: Impenetrable SR, inability to see invisible. Yeah, our summoner is likely to just
magic jar one and have a pillow fight until they get suspicious, then Andre walks in and uses his huge...Diplomacy skill.
Pair of Beholders: While their eye beams are supernatural and thus don't deal with Andre's SR, the DCs are in black swan territory. Even were they to kill Andre this way, there's a 75% success chance of one being possessed by The Gyoji and finishing each other off. This is without taking into account summoned backup.
Gelugon & Iron Golem tag team: With the same lack of the ability to see invisible, while our glabrezu acts as scout and cannon fodder, Andre is still jumping in while the iron golem is boxed in with an illusory box by one of the other summons or even The Gyoji with a spare
wand of silent image. Even presuming it got an attack in, it's not capable of one-rounding Andre.
We've got 9 creatures off of the list so far, and every single one is a hat trick of defeat. Less than half of them even use The Gyoji or his bound fiends to join in as more than cheerleaders. The Same Game Test could literally look like the Monk's training montage of failure for the rest of this, and we'd still be at 50% success rate and thus passing the test as balanced. As it stands, I'm going to guess the summoner
won't suffer catastrophic brain damage and only gets mediocre results at best for the rest of the SGT; which gives us a very rough approximation of 60% to 80%+. This is proper wizard territory.
We've still got over 40k worth of gear to spend on weak spots, half of the Gyoji's spells to be picked out, and I'm not even efreeti wish spamming for inherent bonuses or
simulacrum abuse. So as far as casting goes, the summoner is set and has level appropriate casting of spells with intense flexibility out-of-combat and level-appropriate in-combat. The eidolon is essentially a level-appropriate fighter, who I'm certain is better at grappling than any PC could hope to become or even get through
planar binding.