Do you also have a campy bottom bracket? This could get really expensive. Unless you really are set on campy, I would say just get a set of sugino's or similar. I have both a Campy and a Sugino Crankset on my 2 rides, and they're both great.
FYI - i bought a 165mm SR pista crank just like this one (except the length as noted) 8 months ago and it went for $275. i've since realized i'd be happier with the 170mm so i'm thinking of this crank as well, and then re-selling the 165mm crank. of course, this current offering may go for much less, but i've watched these things closely over the last year and NOS SR pista cranks always go for around $250. i don't know if that's what they're truly worth, but it's what the market will bear.
if i get this one and you're interested in the 165mm, we could talk a deal - but it would be around $275 since that's what i paid.
Is 5mm really a big difference? I've only ridden on 175s so I'm not experienced
Some people say no, some say yes. I say yes, I definitely prefer 170's over 165's. Borrow a friend's bike with 165's or 170's and you will probably be able to tell the most when out of the saddle and sprinting or going up a hill, that's when I feel it.