Ok, I let a tangent run away from me, I'm gonna keep it there but its pretty irrelevant (and long-windedly useless).
125 Should be fine, we've already got folks dominating research/construction/summons at turn 44. From then on its just strategy. 40% are out already, another good chunk will be out by 80 and by 125 I bet the remaining 5-10 will be sick of the micro
I passed my goal of turn 20, not going to win, so I'm good whenever.
Tangent Ramble
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Even though I suggested turn 60 earlier, I was thinking along the lines of future games where it would be like a distinct subsection of the whole.
62 nations, many never see each other physically, but hear about their activities. Diplomats get sent, trade agreements, etc. 60 months pass and a whole lot of stuff happens, maybe a very peaceful corner just plays tiddlywinks while the rest of the world is embroiled in war. Turn 60 (more likely 80), everything gets tallied, winner declared and everyone finishes it off single player while the next game is set up. Possibly have multiple winners, highest research, provinces, income, etc. Start a "big board" to keep score and update it every couple of months.
Variations of that would be a Early Age, Mid Age, Late Age scenario.
Early Age - this game, everyone starts at 0 on everything
Mid Age - 40 nations, Start with x sages to simulate research, x provinces, x gems/known sites/etc, x gold/pop, x turn global NAP. Try to simulate turn 40. Ironhawk had a couple games like this and they seemed fun.
Late Age - 20 nations, x sages/gold/provinces, etc and then go at it after x turns. Try to simulate turn 80.
Possibly even run it as a tourney... hmm.
When the early (perpetuality-type) is down to 40 players, stop and declare winners. Winners get a gold star and a hug from KO.
Start up the "mid-game" with enhanced starting positions to simulate turn 40. Everything is nice and clean, very little micro, tons of cash to play with and a set of turns to do so. Play until 20 are left. Once down to 20, declare winners, get yer hugs.
Start up a "late-game" with those 20, simulating turn 80. All your research is advanced (tons of free sages or a mod), upkeep is manageable, everything is clean, set everything up like you want, etc. Gives everyone a renewed chance at summons/artifacts, new sites, etc. Play down to 1.
A few weeks after the mid game has started, start up another early game, rinse, repeat. Or possibly skip the whole Mid-game idea and go right late game.