I would absolutely upgrade to the 11-28. The 50x11 combo is faster than the old 53/12 and the 34x28 will be much better. (12% better) .
Nashbar has the cs 6700 11-28 for $68.99 (avail 8/10) with free shipping for today and tomorrow.
Any serious climber on that type of terrain would use this combo.
"If you think you wont need that low of gearing you just haven't explored enough"
Enjoy the event!