Well, the 600 grit gives a fantastic edge once the stones have broken in a fair amount, but I know what you mean 🙂
The Pro Pack adds the 800/1000 grit diamond stones and a set of strops, so that’s a good starting point. Many people suggest and swear by the ceramic stones also, which are 1200/1600 for the Superfine while the Micro Fine set are stated in microns much like strop compound. As a Pro Pack owner myself I’ve found that the stones wear in very well and my biggest issue is that between the 1000 grit and 5um diamond paste strop is a big jump, so it’s not really possible to get a mirror finish without a lot of work on the strops. It might be worth pondering getting more than one set of strops right away if you want to bridge that gap and save some time polishing.
From there the sky is the limit really, you can start adding waterstones and finer strops on kangaroo and nanocloth as you go if you want to keep expanding your kit!