Read some reviews. 250+ fsb is common for these boards.
I'm at 10x240 with a Mobile 2500+ and Mushkin Black Level II PC3500 with an SP-97 and a 92 MM Vantec.
The highest I've tried so far was 255 fsb, and that was no problem, but I didn't want to run my vcore so high ( i keep it at 1.825 volts - 31 idle 37 prime tortue load; 35 gaming)
-EDIT- The ClubOC.net review is excellent. They broke 260. Also, some forums have people who have gotten 270 fsb and even 283 on these DFI's. These boards are 1000000000000x better than my old NF7-S in every way.