I may question if you can get the cut of SF4000 with SF4500, but I bet you can get the finish of SF4500 with SF4000 (within higher frequency). Got it?
4000 is rated 4 / 10 (cut / gloss) scale, while 4500 is rated 2 / 10. This fact (in my understanding) tells that they start cutting differently, but will end at the same finishing capabilities. Right?
If you only have 4000, my suggestion is for you to get the softest pad you have available, and work the whole surface again with this setup.
Play with polisher speed and pressure... you may want to put very little to no pressure at the ending passes when finishing (and abrasives are properly broke down). Polisher speed may vary, but it's not the fastest (speed 6), aba not the slowest... you'll need some polisher speed and some pressure from the start to work the abrasives properly. SF4000 works good at speeds 4-5, sometimes 5 finish even better than 4, unfortunately this do not means you may not use it at speed 2, 3... above are just suggestions.
If you finished SF4000 on white pad properly (and paint is also not the damnest softest paint ever), it's hard to notice a difference if you follow with a gray / black finishing pad.
By the way when I'm trying to reach the upmost, I will 'execute' the last step with the softest pad anyway because maybe in the end, at some angle, it may give that 0.001% more shine we are all after!
Keep in mind when you are polishing the paint, you're actually 'micro-scratching' the paint with the abrasives. The finer / softer you go at the end refining your 'micro-scratching', the more improved will be your finish (considered your correction work was done right).
In this case, if you can have both (SF4000 / SF4500), SF4500 and the soft pad would be the likely choice for final finishing because it's even finer... if not, SF4000 will do the job 99.9% of times.
Again, read my comments with care without literally trying to reproduce anything I've said. I've tried to use some keywords for you to look after and try to improve 'your own way of doing it'.
Hope that helps,
(please, ask if needed),
Kind Regards.