So, at the moment im playing some Diplomacy rounds with a friend of me.
At the moment only agains 8 Normal AIs, because he has to find "his" way to play.
Hard AI would destroy him atm.
We use a Galaxy with 5 stars and 2 players per star, also with something about 30 planets per star.

But:
After a while i build up a big fleet.
Im Advent, so im using mainly Drone Host combined with Guardian. If the enemy uses also Carriers, im sending some Defense vessels with them. also some other ships for different situations. Capital Ship is first the Mothership, second the battleship or Carrier.
But if i have this fleet, the game begins to lag extremly. Play 10s -> 15s lag
If i play Solo everything is fine, my computer is not bad at all
i5 2500k running at 3,3Ghz - 4Ghz
4Gb DDR3
Gainward GTX560Ti 2048Mb GDDR5
so, not bad, no problems.
But his computer is something about 6 years old. Dont know if Sins cant handle these fleets in MP, or his Computer is too slow.

So...the primary question is:

Is the performance in rebellion better then in Diplomacy?
Or is it lagging there too?

and secondary question:
What do you think is the problem with our game? his pc? Sins itself?