To the OP`s question-
(Very valid responses above)
Yes, Speed is certainly an option to use after Cut. The caveats being- what are your goals and how does the paint respond? Filling is a larger possibility with Speed than Polish but any product can `hide.`
Troy mentioned Speed being a mix of Polish and Poxy. I believe that to be mostly correct, however, I believe Speed was also `updated` when HD revamped Cut and Polish with the AAT abrasives (thus- Cut+ and Polish+.) I seem to remember David F. saying that Speed had a small percentage of Cut added to the mix to help with defect removal and also more Poxy for longevity... therefore a overall reduced amount of Polish as a % of the mixture... I could be wrong but that is what I remember. (Dig around in the 3D/HD sub forum. Info should be in a post probably from early 2015 or thereabout.) In my experience, I believe Polish+ holds the edge in overall aggressiveness vs. Speed. That being said, I would wait until David F. stepped into the conversation and cleared the air before trusting my words 100%.