Originally Posted by Road Fan

Yes, you pretty much got the idea. Get a ruler that reads metric at the hardware store - General brand has a really convenient 6" one for less than $10. Measure how much farther down your rear brake shoes can be moved. If you have at least 4 mm, you can fit 700's without replacing the calipers.

To commute, you need a bike in good condition every day. Can you achieve that with older wheels? Only if you can resolve problems as they occur. If you start with a new or lightly used wheel or rim, your nightly issues are likely limited to light truing or routine adjustment or inspection, outside of slow leaks. If you start with used wheels that came cheap, all bets are off even on Ebay, unless you have the skills to assess condition.

And rims are critical to safety - you need to get to work, AND get home.

I'm not sure what you mean by "get a ... 10 speed cassette on the RS80s." Didn't you say those wheels have a 10 speed cassette (NOT freewheel!!)? If you need a cassette, that price goes into your conversion cost, though I don't know that price.

What do you mean, saying the RS-80s are carbon/aluminum? Carbon rims with aluminum hub? It does not strike me that carbon rims are suitable for a commuter, depending on road condition, but I don't own any so somebody else should chime in on that. I'm not against using racing gear, I commuted on tubulars in Chicago on 32-hole box-section rims many years ago. But aluminum rims fail by bending, and I'm not sure if carbon rims fail that way.

Re: 20 speeds, why not? If the chain is not too wide and the rear derailleur is set to traverse the whole width of the cassette, your old parts should handle it just fine. And the questions about chainring size - what's your concern? There is a chain length-setting issue which is not actually difficult but requires that you know how to find the correct number of links - it can be done by math or by test-fitting. As far as what gearing should you have for commuting, we can discuss that if you need to. Should decide on the gearing requirements before you cut the chain.

By the way, I would not expect local bike shops to readily get their minds around "will this work?" If one does, you have found a shop worth sticking with. The only way to answer that question for sure is to do it, find the problems, and solve them. Then you'll be the expert.