Actually, the Borg "transwarp" conduits don't enable Warp 10 speed, as has been stated on screen in TNG and confirmed visually on VOY. They actually just accelerate the ship to somewhere around 20 times faster than maximum warp (although from the VOY evidence, I'd say probably faster than that - the Delta Flyer went nearly 10,000 light years in about an hour or so in Dark Frontier - fast but nowhere near "instantaneous" as Warp 10 would be).
"That might have been the biggest mistake of my life..."
"It is unlikely. I predict there is scope for even greater mistakes in the future given your obvious talent for them."
Vila and Orac, Blake's Seven