430mph at level flight according to most stats I've seen.
The problem with the F2G was that, unlike the early-model Hogs, Goodyear didn't have time to work out the kinks before the war ended and the project was abandoned. However private racers took over the job and the F2G absolutely dominated aircraft like the P-51 (clocked at 470mph level with a 4400 fpm initial rate of climb).
So I'd say it's unfair to judge the Super Hog based on the performance of the prototypes, and one REALLY needs to look at how she handled once her rough edges were smoothed over to get an idea of how the actual production model would have flown.
I'm not saying the final production F2G would've quite performed at that level (I don't know all the modifications made by the racers) but it certainly would have been one wicked machine.