3D Mark Vantage seems to be more unforgiving than 3D Mark 11 when it comes to aggressive overclocks. My 570 was at 800-810 I think it was but would crash repeatedly in Crysis 2 (dx11 mode only) and 3D Mark Vantage unless I clocked it down to 750... that's been my experience... one speed may not be so great depending on the title.
If you ran 3D Mark Vantage, 3D Mark 11, PC Mark (version whatever for overall system stability), Aliens vs Predator, Heavenly, and any other game benchmarks you like or have available, it'll probably be ok if its stable throughout testing (even if it's not, it may be a driver issue, so re-test with slower speeds to test)... Heat is the main killer... I'd focus on that mainly.
(950/1900/2100) is exactly what my Gigabyte 560Ti is running aswell, with 1075 vcore.
Runs very nicely for a 24/7 overclock each time i push towards 1GHz i have to really ramp the voltages up and the temps go a little high for my liking. 950MHz core gives me max temps of like 66-68 when gaming and 72-73 when stress/burn in testing.
mines currently running pretty stable at 1000/2000/2240 at 1.050 volts under load and 0.950 at idle. temps are at around 72 under full load and fans dont go past 58%. hopefully temps lower when i get my new case fans. im still testing these settings and if there are still crashes then ill be lowering the memory by about 10 each time until its 100% stable (im pretty sure it will be stable at 2200 mem unless its already stable at 2240
on the 570, i couldn't find any benchmark run that showed any difference running the memory at 1900 or 2100.... that was a crap pny model that i couldn't even tweak the bios file for changing voltages though... pretty much hard-locked to do little more than stock. bottleneck was elsewhere i assume.
i'd like to know the results of any experiments you might have done, specifically with the memory speed....
Anything over 40 fps really isnt going to make very much difference. With 60 being the absolute optimal. Your probably better off just running a lower OC and keeping your temps lower. You can always clock it up again if you find a game where the frame rate struggles.