Profile only accounts for so much. My big box can run the game on the 17 ms profile up until the numbers get high.
Once that happens, the game adjust settings on the fly (anecdotal evidence) until you either clear the wad of ships causing the slowdown or manually adjust the profile. The you come to where once you hit the 117 ms profile and have a ton of ships that you can't clear fast (or in my case, you own) and the game starts lagging on its own. You haven't lived until you have to play out a large scale battle at under 1 FPS.
If you can keep the AIs fleets relatively small then you can avoid most of this though.