I'm nearing the endgame and experiencing an increasing number of crashes when in tactical missions (The Geoscape runs as smooth as silk). It becomes all stuttery and then locks up. Usually there is enough time to exit, but the mission will usually crah again anyway. What is causing this? Is it save game corruption, or does the game have issues with the late-game units?

Win 7 64 (SP1)
Core i5 2400
ATI Radeon HD 5770 1 Gig VRAM
8 Gig Ram

I have tried setting CPU affinity and turning off shaders, that doesn't help.

Found a workaround for this, but it's not a solution. If you just take 6 soldiers, the tactical missions crash much less.