IIRC, posted speed limits within the Federation are somewhere in the range of warp 4-5, because anything higher makes rips in subspace, which can cause some sort of mayhem later. Starfleet ships of course, are allowed to break the speed limit, at the discretion of the captain and/or orders from Command.
The Intrepid class starships introduced moving angled warp nacelles and this supposedly minimized the effect on substance, cancelling the warp 5 limit...other ships had fixed angled warp nacelles or were modified in some way to lessen the effect.
He was also in a 900 page book by Peter David, "Q Squared."
Good Book!
Warp Speed
Warp 10 was supposed to be said to cause a ship to simultaneously occupy every point in space....how the hell this happens I don't know.
Yeah they say that warp factor has been change each series but I reckon besides the last of TNG where there was a warp 13....it hasn't really....consider this for top warp speeds:
Phoenix - Warp 1.0
Enterprise NX01 - Warp 5.0
Daedalus Class - Warp 6.0
Oberth Class - Warp 7.0
Constitution I Class - Warp 8.0
Constitution II Class - Warp 9.0
Excelsior Class (Transwarp Failure) - Warp 9.2
Galaxy Class - Warp 9.65
Sovereign Class - Warp 9.9
Intrepid Class - Warp 9.975
Now, the advances are smaller in decimal places considering the tame frames, but since warp has a sleadily increasing scale, the differences are actually bigger.
The Star Trek Enterprise D technical manual states -
Warp 1.0 = 1x Speed Of Light
Warp 2.0 = 10x Speed Of Light
Warp 3.0 = 39x Speed Of Light
Warp 4.0 = 1??x Speed Of Light
and so on....,
Corm (Geek) Out...