So from what you have said so far you have an R31 with an NA RB30, but in your info it says an R31 with an RB25DET, question is how much power do you have?
If you are still running the NA RB30 or stock RB25 then forget about 300+ rwkw, go with the 25 and aim for 270-280, trust me, i had a fairly stock 25 and was aiming for 300+, had it tuned and hit a wall at 250 but f**k me, 250 is fun and safe on a standard 25 and there will be no f**king around with cross breeding parts that may or may not work well together, stick with the proven path to power its a lot cheaper an easier, on the other hand if you want bragging rights that you have something custom in there then you best start saving lots of money.
As for the bragging rights tho with only 320 my first question (and everyone else i know) would be "why bother".
EDIT
kitty has n00b aids!