Basically I feel that a blitz player will always beat a turtle in a PvP match. The reason is not so much the superiority of one style over the other, but the blitz player will always slaughter the AI factions first, then come after the turtle with a massive advantage in resources. The turtle cannot build fast enough to counter this. ATPG has proved it to my satisfaction.

There are two ways to even this up: multiplayer (no AI) with 50:50 blitz:turtle players and/or, in PvP impose a house rule forbidding conquest of the AI factions (you can defend but not attack them).