Don't worry about the core speed, the card is not fill-rate limited, but memory bandwidth limited. The only improvement you will see by raising the core speed is artificial benchmarks like 3DMark 2000 & 2001. The memory speed is what gives you extra performance in games. Can't remember where now, but a few monthes ago Sharkyextreme, Tomshardware or somebody did a thorough review which included a Geforce Ultra (250/460) and an overclocked Geforce Pro (220/460) and the gaming benchmarks were all equal.