Well in my honest opinion i would go for a new motor. The rb 3 port is a sweet engine I own one and it is great. Now if you go for the V spec it is a very fast engine and hard to get used to being so fast. Now for the p5x that is also a sweet engine. Just take in consideration you driving skills and what you want to get out of the engine. If I was you go for the rb 3 port they are smooth and very reiable. I can tell you that the v-spec is awesome for only being a 3 port.
I just see to many people go for the best and have trouble with the engine of there choice and get fustrated and give up so go for the rb 3 or the nova rossi 3 port and learn from there..