Mazdaspeed does not supply or have any 4 rotors. Unless this is something that just happened within the last 3months.
I had an '06 shinka for a very short while, and IMO, the renesis is a superior engine. Sure it doesnt come boosted, but once ppl figure out the ECU, I am sure it will be a beast.
IIRC, to swap a 13b into your 8 would be a waste, for the money you might as well go 20b and boost it to 600whp. Just like the guys in PR.