Did you ensure most other programs are closed before you run SINS?

Ctrl Alt Del

processes

CPU usage and mem usage

(close include firefox and/or inet explorer)

Then the best I can suggest is playing with fleet sizes set to "small".  This is kind of a misnomer, since fleets can still get pretty big, just not quite as big.

Consider running with normal or slow settings too instead of Fast or Faster for large games.

Yeah, just played with small fleet size, it did help quite a bit.

Will also try slow settings and the processor trick, thanks for the help.

I noticed no one mentioned trimming the empire tree. This can be mainly done before game start to not automatically pin planets, ships, fleets, etc. You can also pin/unpin in game to help trim the tree down. Many people have reported this helps with lag as well.

I keep capital ships pinned and pretty much unpin everything else.

Notice there is a no way to turn off auto pin of Star bases. You will have to manually unpin those if desired.

Sins Optimization Project

The problem with lag is the hardcoded limits in ram usage.  The Optimization project will help solve this issue by minimizing the ram load of the game.  Check it out!