Guys I got a fix from KFA2 support - Change the power management mode in the Nvidia settings to Prefer Maximum Performance.
This completely fixed the issue and my drivers arent crashing anymore in any game.
I already tried all 3 of the latest drivers, 304.48 beta, 301.42 and 301.34, only after I installed G+Ks this problem started happening gradually more and more until it broke all my games.
Currently I'm running 301.34 drivers and changed to 'Prefer Maximum Performance' and this has fixed it in all my games. The graphic driver was previously crashing everytime GPU boost lowered the clocks, I discovered this from playing Guild Wars as this was the only game that temporarily locked up and then resumed working again instead of just crashing and using Afterburner monitoring graphs:
1) When the GPU + Memory would sharply underclock due to GPU boost, I would get significantly long lag spikes with a frozen screen and occasionally a black screen within 5 minutes of loading the game due to the 'driver stopped responding' crash, after which the game would resume working.
2) After the driver started working again, the clocks would stay stuck permanently at their low settings of around 324 Mhz for both the GPU + Memory.
3) All other games would simply crash when the driver stopped responding.
I sent this info to KFA2 support and was going to add it to the Nvidia forums too but they are down atm, and I dont feel like typing out a full email to Nvidia support instead of just posting the fix into current threads.
I was stressing the card at its previous maximum overclocks of 1240 / 7200 Mhz and no more crashes in Heaven, Civ V or Guild Wars so far, so all looks fine.