Mine is Upreved already but is going back for more work soon... and Decats dont rasp, well good ones dont!
Am guessing that you have a y-pipe with the nismo but if not, go with the motordyne y-pipe with swapable cat / decat sections. Saw one today, lovely made bit of kit!
If you run uprev with maps then you can go with decats as you can use a map for the mot Speak to Mark about it...
Mark