Having just converted a triple to a compact crank on one of my 5 bikes, I have learned a lot.

I needed a 165 mm 9-speed crank for my short legs. The only model available was the Shimano Sora. I liked it -- much lighter than the Truvative triple.

FSA 9-speed compact cranks only come in 170mm lengths which would cause me too much toe overlap with the front wheel.

The compact crank works with a double front derailleur and triple rear derailleur. I replaced a Shimano Tiagra triple front derailleur with a Shimano 105 double front derailleur.

The compact crank must mate with its bottom bracket. I replaced a generic Truvativ triple bottom bracket with a Shimano hollowtech.

The Shimano 105 triple rear derailleur works perfectly!

Depending upon the other components -- 10 speed or 9-speed rear cassettes and shifters, the compact crank doesn't need Ultegra level, especially if the rest of the compenents in the drive train are less than Ultegra-level in quality.