high-end Al or low-end carbon?



Hi all,

I started riding roadbikes 2 years ago, after 20 yrs of nordic skiing
and racing. Back then I got myself a Felt F70 for $1K and, as I was
learning, ended up ugrading it (all 105) with Ultegra-Dura Ace and
Ksyrium SSC SLs. I am 175 lbs and 6", and I like mashing gears going
uphill, so I appreciated the stiff ride of the Ksyriums and of the Al
frame. I was happy with my old good Felt F70.

The F70 got stolen last week and I am on the market again. I am looking
for a stiff frame which would preferentially have a lifetime warranty,
with at least a full ULtegra. 9 speed components are fine. Ti is not an
option, tried it, too soft. So I figured I would stick with Felts. I am
trying to fit into the 2K range. Felts come in Aluminum up to F55
($1.7K) and then become carbon at F4C. So the question is - what's
better, a low-end carbon frame, or high-end Al frame? Better means
stiff and break-resistant. I Don't care about weight. BTW what is
low-end carbon frame? Felt says F4C is 3 layer carbon while higher end
felts are 2 layer carbon. Is that all the difference?

These are the specs for F4C. http://www.feltracing.com/06/06_bikes/f4c/
WHeels suck, the rest looks fine, except that carbon frame which I
know nothing about.