Originally Posted by Revs
When I set mine over 740, saved it, closed RT and opened it again, it said 740. Anything over 740 would reset to 740 after reopening. It might be different with a newer version though.
Its not Riva Tuner thats limiting your core OC, its your shaders. You need to bump up the shaders a little more and then try to OC the core past 740 again, if it bumps you back down then move the shaders up a tad bit more and try again.
The previouse Gen cards G80's and G92's were not dependent on the shader for the max core overclock, its a bit different with the GTX 260 and 280.