Why would you want to spend all this money upgrading an already decent set of TruVativ cranks? It'd be less hassle, and a wiser use of the cash to spend your money on a decent set of wheels.
I'm guessing as it's an 08 Pista the bike is pretty much new, you could wait until the chainring/sprocket/bb starts wearing out, then upgrade to the 75.
I just got a set of TruVativ Omnium's for 08 Pista and once the rest of my bike arrives I look forward to testing them out. Overkill for street use? definitely.