I am (was) facing the same decision. Even though I haven't bought them yet, I have decided to go with the Studio 60s. I listened to both of them at a local dealer and as far as sound quality goes, it wasn't even a comparison. There was so much smooth detail coming from the 60s that I didn't even need to hear the Monitors. I listened to them anyway just to give them a fair shot but it only confirmed my impression of the 60s. I personally would have no problem listening to music on the 60s without a sub - unless it was very bass oriented music like rap, etc... I was actually looking at getting the Monitors with a sub or the Studios without a sub (for the time being) and I still have to go with the Studios. These were version 4s that I listened to as well. My vote is for the 60s all the way.
Matt