Ok. In my opinion the main differences will be in power delivery (full akra on hp4) and the DDC on the hp4 compared to the standard setup on the regular rr. The feel of the DDC is that the front is always planted and grippy because the damping is more responsive, but the standard bike is bloody good too. Power wise both feel insanely fast and plenty good enough for me. It's really a case of budget and preference. I'd choose the hp4 only because the DDC is that good, or wait for the DDC option on the rr which must be soon? The only other consideration would be that the hp4 bike is a two year limited production, buying one new is not going to be an option for much longer.