Edited that post with the Galaxian Empire's current batch of starfighters, the Walküre VII.
Also here's a quick explanation for the imperial warp classifications.
Warp 1 means the speed of light or circa 300,000 km/s
The numeric part is the exponent so for example Warp 1.2 means 300,000^1.2 or about 12.5 times FTL.
The fastest starship drive in the Galaxian Empire is about Warp 1.7 which allows a ship to travel 18.7 lightyears in a day.
For expressing more slight differences in speed the Galaxian Empire uses the "sub-warp" figures which literally only tells the speed difference between you and the other ship expressed in the fractions of the warp factor.
"Sub-warp minus three-point-fifty-five" with the speed of for example Warp 1.55 means the other ship is moving at roughly Warp 1.495 so they can catch up to the other ship from 10 AU away in a bit less than 10 hours.

Anyways, you really-really don't need to think much about this.
Just take it as a random technobabble.
I don't think I'd always do the correct math either. Just say what is roughly appropriate by gut feeling.