tp4tissue complains about the slowdown the game has when there are 100+ units on the screen playing on ultra settings on a 30 inch monitor @2560 x 1600
its not an FPS issue
http://www.legionhardware.com/articles_pages/starcraft_ii_wings_of_liberty_beta_performance,4.html its a CPU issue and every single RTS has the same issue late in games where there are hundreds if not thousands of units that the AI has to think for. Civ was horrible at this.
its also a non issue
You are totally missing the problem of the end-end-game slowdown. Destroy 90% of the AI's units and you could encounter massive stutter. After your stated "hundreds if not thousands of units that the AI has to think for" have been mostly destroyed, the AI goes in the think tank trying to come up with a plan to replace them. With drained resource fields, this becomes an impossible goal, and the AI algorithm tanks the CPU performance just "thinking about nothing". The only way to remove the stutter was to completely eliminate the AIs final building. This was really noticeable in 1v3AI and 1v4AI custom games.
It is NOT a CPU issue, or even a issue that other RTS have. It is an AI algorithm problem. Apparently you spent all your Beta time playing ladder games, and none of your time trying to be an Accomplishment Whore(tm) by playing the "outmatched" custom scenarios against multiple AIs or by playing against any of the Insane AI settings.
It is only a non issue if you never play against the AI.
Edit: Blizzard has announced that they started to investigate this issue, as of last week.