Improving condition and setting reasonable goals

Hi everyone,

I consider this a "tech" question because it has to do with the
mechanics of the body. If anyone can suggest a better NG for this,
please do.

I have been back in the saddle for about 9 months after a several year
hiatus. My condition has improved quite a bit during this period. A
certain 10km rolling out-and-back that took me just under 21 minutes a
few months after I started and now can be done in just over 16 minutes.
The old times were done with a HR around 155. Anything above that was
not sustainable. Now I seem to have an upper semi-sustainable limit
(for 16 minutes at least) of around 180.

I usually ride a minimum of 8 hours per week spread over 3 days (2
hours, 2 hours, 4+ hours) but some weeks only 6, others much more. I
have completed several 200+ km rides withou being miserable.

My results have not been planned or goals to attain. I have just
ridden, and observed the results.

But now I would like to set some goals, but I want to be realistic
about what is attainable and in what time frame. My goal is 14 minutes
for a flat 10km TT. Is this attainable with 8-10 hours per week? What
is a reasonable time frame for such improvent?

I push slightly heavy gears and in the old days I used 180mm cranks but
have recently switched to 175's and I try to spin more, but I'm not
really built for spinning. Years ago my thighs were about 28" around
but now they are 25". I notice they are growing again. Is there any
sense in trying to limit their growth somehow? I suffer on climbs due
to my weight, but most of that is from dead weight from fat and upper
body mass. Is there any advantage to be had from having a few extra
kilos of muscle on my thighs? Will larger muscle mass hold more
glycogen allowing me to push my limits for a little longer (and maybe
not get dropped immediately on a climb), or will the extra weight just
be detrimental? Even if I wanted to, could I limit growth?

Suggestions?

Thanks,

Joseph