I usually play 3-4 AIs on a medium sized map (somewhere between 30-60 'planets') and can play for over 10 hours on highest settings with BailKnights graphic mod with little or no lag. The new patch 1.2 has helped this a lot. Also, running few other programs can do wonders. It depends on what your specs are tho.

Generally speaking, if you're expecting the game to drag on for hours on end, you should choose small fleet sizes.  This helps performance enormously once everyone has massive fleets of doom.  Aside from this, you can try setting all the AI's to aggressors.  One of the big performance hits with 10 AI's is that they'll set up minefields on all their front-line worlds.  This is a double-whammy, crippling their fleet (minefields are stupidly expensive) and preventing them from attacking, while filling the game-universe with thousands of tiny objects taking up valuable system resources.  The AI is obscenely defensive in general, and this means given enough time the map will become a sea of minefields, starbases, and maximum-sized fleets, so setting them to the more aggressive setting can definitely help.

Now, it's entirely possible to play 10-player games on massive scenarios, but you have to play aggressively.  If everyone's allowed to build up to max-size, it's going send performance down the toilet.  If you really can't kill off any AI's (you can't count on them killing each other, sadly; the AI is quite an incompetent attacker), you probably should keep it down to 6 players and 60 planets.

Huh... those stats are better than mine. But that is 8 players for 7 hours. How many 'planets'?

No one else has input for this?

What size maps do you all play, and how long do your games go?

The worst situation isn't when you have a slow computer...its when someone in your LAN party has a slow computer, and everyone else is fine...it's in these situations where lag seems to reach a whole new level...

Weird things like damage being delayed for minute +, sound/graphic effects for weapons and abilities not appearing, etc...

Had a game where my fleet was sitting just outside the range of a Transcencia's meteor storm...problem is, one of my ships for whatever reason got in range while forming up which allowed the guy to target my entire fleet (range of ability and range of buff are two totally different things)...I'm sitting there for 2-3 minutes watching my fleet while managing construction from the empire tree when suddenly a 1/3 of my ships just disappeared...literally, just gone...I had no idea what was going on but I got the hell out of there as fast as I could...

As I found out after the game, apparently the guy had hit my fleet with meteor storm 4 or 5 times...yet, I didn't see any effects and didn't see any damage until it was already too late...it was weird as could be, some of my ships had no damage while some just disappeared...even weirder, some ships had hull damage but had a lot of shields left (I didn't have a prog so how that happened is beyond me)...

No...my ships were disappearing and registering damage while sitting still inside a gravity well...

There are only two things that could quickly cause massive amounts of damage to entire fleets instantaneously: meteor storm, and kostura strike...since kosturas have now been changed that obviously was not the case (and they never built one anyway)....

It's not a bug per se...the other team saw the effects and damage in real time...and eventually I saw the damage (and the resulting losses) later...the reason why damage was not consistent throughout my fleet was likely because not all ships were hit by every single meteor storm strike (most were outside the range of the ability anyway)...

A similar situation happened earlier in that game with malice...the damage from malice was not registering in real time (for me at least)...the enemy fleet was focused on targeting my capital ship so without malice that would have been the only ship taking damage...since I didn't see malice ever being used I figured his prog just had shield regeneration and colonize on it...suddenly all my frigates starting registering large amounts of damage and I lost most of them before leaving the gravity well...apparently, he had been spamming malice the entire time though I never once saw the effect (though I did notice his prog never had a lot of antimatter)...