I'm a KFA2 (Galaxy) graphic card user as well - I've got 660Ti model EX (factory OC-ed). Maybe my post wouldn't help, but it's worth to try.
KFA2 cards have strange "feature" - mine was advertised as 1006MHz core with 1089MHz turbo, whereas it turned out max turbo is 1189 (!?). It looks like turbo works beyond advertisement
but a negative impact it causes might strange behaviour like spikes, hangups, or "graphic driver stopped working, and has recovered". I experience this last one only. All would be (probably) fine, if engineers took after proper core voltage with such high turbo level.
All I suggest is to turn Afterburner on, and decrease core speeds to 1046, for both cards respectively. Just for 100% be sure you might add +50mV to each core. And check your games then.
By the way, people report SLI consisted of such two strong cards works better with i7 (comparatively to i5) CPU due to CPU high usage in some games, including BF4.