LOL Voyager 1, in "normal space", without warp drive or time acceleration, is currently at 17,260 m/s.
Not that it's in any way 'limited' to that speed, of course.
Besides which, motion is of course relative - we could measure V1's speed relative to anything else, anywhere, without physically causing the craft to accelerate or decelerate itself.
And the only reason it was able to reach that speed is because it was also able to do real-time planetary fly-bys, without "orbital cruise" and "glide mode" transitions robbing it of all its velocity..
But hey no, "boo spaceflight!", and "yay custard physics!"
I also have an Eagle in ED. My only ship in the game. It can reach dizzying speeds of up to 170 m/s. Do i care about 'upgrading' it? Are you kidding? 170 m/s or 870 m/s - what's the substantive difference, in spaceflight terms? Zilch. Either way, it's not moving, helplessly marooned stationary but for its "supercruise" warp drive.
I have another Eagle, in FFE. Top speed? Zero. No 'top speed'. It does have a nice delta-V tho - 28 G! And no matter how fast i go in it, it always still has that 28 G of thrust! It can fly from Earth to the Moon in about an hour! In real-time (no time acceleration), without "supercruise" or any kind of warp drive... i just take off from London, point it at the Moon, open the throttles, sit back and watch the speedo climb and climb and climb. Still climbing. Always climbing. Until i cut the thrusters. That, my friends, is spaceflight. That's a 33rd-century fusion-powered Eagle Mk III! Shocking huh?
Bet this sounds utterly lame if not terrifying to the average ED player..