That board was used in Dell's earliest quadcore workstations such as the Precision 390. While they never came with them, userbenchmark shows many people running quadcore Q6600 and Q6700 (they originally only came factory equipped with Core 2 Extreme quadcores) which are pretty much the same as you have now, only with twice as many cores and cache
While Q6600 is easily overclocked in later Dells to 3.0GHz with padmodding (Q6700 to 3.33GHz is far less likely), the 975x only supported up to 1066FSB so that wouldn't work, plus even with full voltage controls in aftermarket boards it required some pretty alarming voltages to reach even relatively low overclocks. That's because it's so old that it was originally developed for Pentium 4 (where only the Extreme Edition was 1066FSB), and was made on the 130nm process node
So there is just about zero chance it would support a 45nm processor, using a 1333FSB that the chipset doesn't support, and 65nm 2.67GHz quad is as fast as you're going to see in that board. I understand some manufactuers like Abit did add support for 45nm chips and their half-multipliers (Q9705 is 9.5x) in their very last beta BIOSes for 975x boards, but Dell would never add stuff like that even if their board OEM did.