50-34 Compact conversion?
 

I have a 2001 LeMond Zurich with Ultegra 9-speed. The crankset is 53-39 and I'd like to get some better climbing gears. Will the current Ultegra 10-speed crankset and external bearing BB fit ok? Do I need to use a 10-spd chain? Also, is it worth the extra $ to buy a 12-27 cassette to use instead of my current 12-25--would 2 lower teeth make a diff worth it? Thanks.

The current-gen Ultegra crank and BB will fit. A 10sp chain would be best. You know how your chain will begin to graze the side of the big chainring as you shift to your outboard cassette cogs... well, that gets more pronounced when the big ring is 1.5x the size of the small ring, not to mention being spaced for 10sp chains. So a narrower chain will help.

The 12-27 would be a good pick since your goal is easier climbing gears. The final two shifts are three-tooth jumps instead of two-tooth jumps, so your flatland gears will stay the same. Getting a new cassette will also ensure you don't have chain skip due to mismatched wear levels on the chain and cassette.

If the 50 x 12 high gear isn't high enough, you could also opt for an 11-28 cassette, but then you give up your 15-tooth cog, with a 14-16 jump that might be an annoyance.

Alternatively sticking with the 9 speed chain, you can get [say, 1.5mm thick] shim washers
to go around the 5 chainring bolts. move the inner ring, a bit wider gap between the 2.
so you can shift to some higher gears on the 34t..

I dont up shift from 34 to the 50, (> or 36 to the 52 in my case..
but at the crest of the climb..

Thanks! Great advice all around. Can't wait to set it up.

Following up with results...I had it done utilizing an Ultegra 10 spd crank (couldn't find a 9-spd), an Ultegra 12-27 9-spd cassette, a Ultegra 10-spd 6600 chain. Went on sweet, cassette shifts pretty good--there's a scant few times it's chattered shifting into the lowest gears but not that big a deal--could need to wear-in a bit or better tuning on my part. Smooth shifting up and down on the chainrings. It's nice being able to spin up the steeper stuff I was bottomed out on before.