If you don't mind me saying so..... running 75's on a commuter is going to be some costly overkill. If you are doing this to end up with "Real" track cranks with 144 BCD then that is your business.

As a note, if you are looking to get into real track cranks most of the quality track chainrings start at 46T and up. A rider on the track would have no real use for a 42T ring. If you look you will see that the 42T chainrings are almost 100% resigned for used with 130 BCD cranksets.

The only one I can think of that is 144 BCD and comes in a 42T is Sugino's Zen Messenger ring. Their are a few 43 and 44's out there but the choice of a 42 is quite limited.

What size cog are you running? If you are starting from scratch you may want to get a more standard track chainrings size that is still cool for the street (like a 46-48T) and then get a cog that is more suited to the gear ratio you want to ride.

Oh, are we talking 1/8 drivetrain? On Bianchi's site for the 08 Pista is doesn't state if the crainring or the cog are 1/8 or 3/32 size but the chain listed (KMC Z610H) is only a 3/32 chain according to KMC's Website so, one can assume that the stock cog and cr on the bike are only 3/32 as well.

So, if you go with the 75's you have one choice for a 42T, 1/8 chainring, and have to get a new cog anyway and a new 1/8 chain on top of the crank arms and new bottom bracket. In effect you are replacing 100% of your drive train! If you are gonna do that, move away from 42T and find another CR to Cog combo that gives you the gear inches you want to ride.

Look at Sheldon Brown's thoughts on gear ratios online, it will be very helpful.