I had the 53/39 and 12/27 but it was 9 speed. I converted it to a 50/34 and 11/32. Again it was 9 speed but in my case I never really noticed the gaps in gears......I just adjusted my cadence to work around the issue. The terrain I was using it on was pretty varied...from rolling hills to long steep climbs. I could see with your terrain going with a 13-28 cassette...or a cassette that gave you tighter gearing. I like the 50/11 for longer downhills where I can still spin at 32-35 mph. However I never use the 50/11 on flats. I know some folks that have stayed with the 53/39 and put on MTB rear derailleurs and gone with an easier cassette just for those step climbs. Some have found a 30 tooth gear that would work with their mid cage RD. The RD specs were conservative and indicated that a 30 would not work but in their case it still shifted okay.

I know all about having the easier gears for the steep stuff. I wouldn't be riding if I didn't have the easier gears!!