39 ring is the sweet spot for solo riding on flats. Except when you really wind it up, catch speed and get to the big ring. I'm not too strong to do that often without cross chaining.

However, if I had a 34 front ring, I'd constantly be switching between 34 and 50 at the front, as I pick up speed (in order to prevent 34-11 cross chaining). I run 30-39-50 with an 11-28 10 speed cassette. For flats, it works wonderfully. For really steep AND long hills, there is the 30 front ring.