J-Field can currently only handle a RTK rate of about 5 Hz. Even it it could process correction faster I don't think you would see much benefit beyond 5 Hz. The faster correction rates decrease the time it takes to acquire a fix when the conditions are favorable. So say the receiver is under a tree with a clear line of sight to only two satellites, it's not going to obtain correct fixes until the satellite geometry changes and the conditions improve. Even if it was possible, increasing the correction rate beyond 5 Hz in these type of situations won't offer much improvement in my opinion.