The 9800xt has no functions exclusive to it; it's just an overclocked 9800 pro.
If the xt has more lax timings on the memory, then getting an xt bios will help you overclock your memory higher at the cost of performance; that's why many people with 9800nps flash pro BIOSes.
Otherwise, it'll just overclock your pro to xt speeds, which is useless.