Transwarp is warp ten.
Infinite speed.
A theoretical impossibility, where you occupy all points in space simultaneously.
The engineers on Voyager figured out how to enter transwarp space which is the only place where transwarp speeds are capable, a higher dimension of our universe, but they do not know how to navigate inside transwarp space or exit transwarp space controlledly.
The Borg cannot fly naked through transwap space at infinite speed.
The Voth can.
Infinite Speed.
What the Borg can do is build transwarp conduits, tunnels though Transwarp space like 19th century man built train tracks across the planet. Transwarp Conduits do not collapse after one use. They can self sustain for an unknown duration without maintinance, or with the aid of a transwarp hub, a Transwarp conduit can be maintinaed indefinitely as part of a mass transit infrastructure.
In TNG Descent "someone" says that Borg transwarp speeds are equivilent to 30 times the highest speeds Federation Star Ships are capable of. The Enterprise was also capable of "unlocking" and using a Borg Transwarp Conduit by imitating a Borg "key" transmission.
I assume that transwarp speed inside a conduit is relatively static.
Laying track, ie building a conduit however seems to a much slower process which is why it took Voyager 2 weeks to travel 30 thousand K light years, but in the final episode Voyager traveled 30 K light years in 2 hours.
As far as flying through transwarp space without a conduit, what takes time is navigating, figuring out where you are, where you are going, and how to get out, which with a more powerful computer would probably make the transition from a to b, no matter the distance seem seamless and instantaneous.
You do know that there is a Trek Tech forum?