i didnt notice u mentioned the stoxx 600 and i was referrin' to the dj stoxx 50 as the one that include uk blue chips issues so i have to guess that the 600 includes uk small caps auto-sectors while the euro 600 just covers europe.
Most of the 600 contracts are very thin compared to the FESX.
I cant see why anyone would want to trade them unless on heavy medication slowing you down, you maybe find it exiting?
Go for the FESX, contract name is now FXU06 or FXZ06 if you want - I do not know the IB names tho (pretty sure they have some stupid codes)