This article is from the Star Trek Tech FAQ, by Joshua Bell inexorabletash@hotmail.com with numerous contributions by others.
Yes. According to the TM and "Best of Both Worlds, Part II", if you're
in Warp you can transport as long as you are both at the same Warp
value. The TM says "integral warp value", but in BOBW2 they were
chasing the Borg ship at, I believe, warp 9.6 or something similar.
H. Peter Anvin offers:
I think the intent of the phrase "integral warp value" means
anything with the same integer number, i.e. 8 <= warp < 9; so in
BOBW2 the big E would only have had to exceed Warp 9 in order to
make this possible. The TM makes it abundantly clear that a
transition occurs at integral warp factors (and we deduce that to
be the reason the warp scale changed between TOS and TNG) so I
think it makes a lot of sense.
Possible. However, doesn't O'Brien say "Matching warp velocities for
transport" or something quite similar? They'd have to be going at
nearly the same velocity already to keep up with the Borg ship, so
matching velocities could only refer to fine tuning.
In "Force of Nature" [TNG], they transport from a stationary ship
while falling out of warp in an area of massive subspace instability.
It could be that since they aren't actively generating a warp field of
any level they can get away with transport.
 
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