First, try -H 2 instead of -H 0. Here's what I use to get ~300 kh/s per card (7 of the same card you have) with a +600 mem overclock (+0 GPU, GPU doesn't make as much difference on these cards and crashes quickly for me with any kind of OC): cudaminer.exe -H 2 -i 0 -m 1 -b 4096 -l T5x24 Keep in mind when comparing overclock numbers with others on this thread that your card is already at +169 GPU and +183 mem over a stock 750ti. Any overclocks you do are on top of that.
So you're doing +600 in addition to the EVGA overclock in bios or including? Mine seems to throw cuda 30 errors anytime I approach +415 in the precision x app. Still have only been able to get 315 on one of my evga ftw cards. The MSI gamer cards seem to get to 298 before giving the same error in cudaminer. Seem like totally stable overclocks besides those errors happening eventually.