Did this myself. You need to make sure your cassette isn't too worn else it won't really marry, likely you'll want to have a 10spd cassette and you may need a new chain. The bottom bracket should be ok (but I replaced mine anyway). Your groupset will also need to be Shimano (105 or better). Your front and rear derailleurs will probably be ok but if your feeling lavish you may want to upgrade these.

The 6750 is the Compact version - the 6700 is the standard. This means that the 6750 has a much smaller inner cog and slightly smaller outer. It is a better choice if you want a slightly easier time of it up hills, but you'll trade away a bit of average and top speed (higher cadence to maintain a given speed). If you're in a flat or rolling hill area the Standard is ok, but if you're in a hilly or mountain zone, make life easy on yourself.

I matched this with the Ultegra 6600 - no problem at all shifts sweetly.

You should check the bike's original spec, easy web search that's what I did. For Pinarello I'd say it would be Italian, this BB comes in both standards.