Hi all,
I play allot of sins rebellion and while playing single player me and my friend have no issues with lag on huge maps and fleet fights. - However on multiplayer through iron, everything is lag free at the start however it gradually gets worse, and when we are maxed out with full fleets we get around 4-10 frames per second even if our fleets are stood still or moving and even fighting, full gfx settings, low gfx settings, It doesnt matter which one of us is hosting the game it has the same result, we both have top end machines which are nearly identical, though mine is a bit better 
Our PC performance is not the issue, we play single player with no issues on full gfx, all ports are open we even tried dmz when playing.
The ONE thing we both notice when playing and looking at the stats, there is a stat which lists a players total clicks (mouse, keyboard) which ever one of us is hosting is normal, say 1000-8,000 clicks depending on the map size etc, but the other who connects... is over 10million we even had one close to 50 million player clicks... which is where i think the problem is as this must be clogging up the game.
Has anyone noticed this or even have a solution?