I was in the shower this morning when a fantastic new idea dawned on me. I was reminded by the TNG episode "The Chase" where Picard made reference to frequent use of high warp speeds having turned the engines into piles of scrap metal.
Ships in STO shouldn't be travelling at warp 9.997 all the time. In the tv shows, a warp speed like this was always described as maximum safe speed, not cruising speed, which was usually anywhere from warp 5 to warp 8. So this is my idea. Speed in sector space at Vice Admiral level should be the same, but be called warp 8. This is the maximum that a ship should be able to sustain permanently.
However, ordering "maximum warp" in emergencies should be allowable. This ability would make one's ship travel at slipstream speed (I personally think slipstream should be replaced by this idea, or make slipstream twice as fast as it is now) but the actual speed would register as warp 9.997.
Now a captain could use maximum warp all the time if they wanted to, but the trick would be that the longer you travel at max warp, the more likely your engines will break down(think of the Excelsior's transwarp breakdown). If your engines break down, they could have a 1 minute repair time followed by max warp being disabled on your ship until you repair at a starbase, or you use a minor component to repair the overtaxed engines.
The most important thing to remember about this idea is that you would still travel just as fast through sector space at cruising speed as you do now, only the velocity readout would appear as warp 7 or 8 instead of 9.97. Maximum warp wouldn't take anything away from the game.
I think starfleet ships now (40 years later) have the capabilities to cruise at high warp. Otherwise the developers would've limited the speeds to lower warp speeds. Slipstreamx2 is way way way too fast, and I'm sure I'm not the only one that thinks so.