The amount of g the aircraft can pull before structural failure is more relevant than dive speed,there doesnt seem to be any information on ww1 planes regarding this but bearing in mind its unlikely that any manufacturer would have wanted to kill pilots we can assume that they were all fairly robust in this department,early models of some aircraft (dr1 and d7) did have reported problems but these were quickly rectified.Sids testing found the following,
d7} halfway to blackout before structural failure
f1}a small visual circle remains before failure
dr1} well past the blackout point
f2b} not yet tested but I would guess midway between d7 and f1.
If all four aircraft g failures were at the same point it would go a long way to evening out the planeset resulting in a more interesting arena.

aka Shotdown