That depends on the spec of the rest of your system really m8.

The way I test them is simple :

I open up Command And Conquer Generals : Zero Hour and start a skirmish. I use the Death Valley map (8 player) and just have me, and an easy army. I start in the top left, and put the enemy in the bottom right.

Start with as much money as possible, and have your army as USA Air Force General. Build an airfileld as quickly as you can, and then purchase all the commanche upgrades available.

I then create about 15 - 20 commanches and then select them all and move them about. Any lagging / slowing down means you'll have to look at upgrading the machine