I'm a terrible climber. Most of it is me, not the bike ("it's the legs, not the bike!"). However, I need to gain just a little more help from my bike then I'm getting ("are you in the lowest gear on that thing?").

I ride a Look 566 with Ultegra gruppo. It's a 50 - 35 compact with (it says on the cassette) CM 5600 12 -25t. On steeper grades (more than 10%), when standing I can just about turn over the cranks, and if I sit - oh, my. My problem is I cannot stand for long, I flood with lactic acid and just die! I need a lower gear!!!

I've done a little reading, and I've discovered that the cyclocross bikes seem to use a 11 - 28t cassette. Lower gear, right? Would that work for me, if I was to change out the cassette on my bike to an 11 - 28t?

Thanks in advance!