[ninjanomnom]

I work on an open source multiplayer game that's limited by single thread CPU speed so I can give a perspective of what would improve for us at least.

The fastest thing to change is we'd increase player limits per server, per player CPU costs are significant and we could bring the player limits to maybe 500 before network speeds start being a consideration. Certain ai improvements that are currently not viable like goal oriented ai design and pathfinding improvements could be added that would make new kinds of gameplay possible. Hell with even just 10x I would be very tempted to try unifying our atmospheric and chemistry simulations so they use the same data structures, thus allowing chemical reactions between gases that aren't basically masses of nonstandard performance hacks on the back end.

In short though, even minor performance improvements would vastly change what we could accomplish. 1000x is extreme and you would see very different games that could make use of techniques that today are mostly relegated to games built around them as a gimmick that they make sacrifices for.