Believe it or not. In principle, the impulse drive should be the same as the ion drive in principles. In practice, the Federation does not have enough real oompf to get the impulse drive working at a decent speed, so they FUSED the AMRE system into the impulse system.
When no warpage or space distortion (and presumably forms of AMRE) is available, Star Trek acceleration is very poor - limited to oh, 1.9km/s/s (Fair Haven.) max. Refer to the ASVS Thread Database.
One really doesn't have to look very far to find the most impressive cases for sublight acceleration in Star Trek or Star Wars. Every time they warp or hyperdrive, the runup (you can see the relativistic distortion) is from 0 to near C in about 3 or 4 seconds (eyeball of distortion) before they transit into FTL state. That implies that assisted, both fleets are in fact capable of MURDEROUS accelerations in the zone of 100,000km/s/s.
Using the same system that makes the run up to warp, one can easily obtain the high accelerations listed in the examples. The difference is that Trek integrates it more into the system, so not every involvement winds up being a full blown FTL trip. Maybe SW integrated it more into their systems too, which might explain why the fighting speeds increased to 0.6C and up in NJO.
It really isn't that much of an advantage for Trek. They'd fight at their usual battle speed (observed in things like STFC) and their high acceleration advantage (if they ever use it, or CAN use it in battle) will be no more useful than their already established ability to warp out of battle and back in Picard Maneuver like stuff. If only one Captain can think of the Picard Maneuver, I doubt the other captains would be fast to use the high battle speed advantage...
By the way, Chris, I thought it was only 500,000km in 15 seconds in Swarm