Have you considered this (quoted from a local bike shop web site).
http://www.granfondocycles.com/specials.htm
Consider the appeal of Compact Drive… Compact drive is the buzzword for a double crankset with a 50 tooth outer chainring with a 34 tooth inner. (A standard double would have a 53 tooth outer and a 39 inner. A standard triple will have 52, 42 and 30 tooth chainrings.) What do these minor changes in your crankset accomplish for you? They give you the light weight and shifting ease of a double, while still having the low gears of a triple. Prepare yourself, here come the numbers… A compact drive 50x34 crankset when used with an 11x25 cassette gives a rider the same low gear as a 30x21 on a triple while still giving a top gear bigger than 53x12. Using a 50x34 with a 12x27 will give a rider the same low gear as 30x25 on a triple with the same top gear as 53x13 or 52x13.
Who uses this kind of thing? Consider that when Tyler Hamilton crashed and fractured his collarbone in the final kilometer of the Tour's first stage, many people felt that his race was over; there was no way a rider with a broken collarbone could tackle the big climbs that were to come. But Tyler had a little help from component maker FSA. FSA supplied Hamilton with a special version of its new 515gram Carbon Pro Elite crank, allowing him to run a 36 tooth inner chainring with a 52 tooth outer. The lower gears helped Hamilton stay seated on the climbs, and recover enough eventually to break away from the peloton on the first slopes of the Col de Soudet and take out a stage win. FSA now offers this same crankset to the general public.
The Compact Drive cranks are easy to install and require a minimum of extra parts. It is easier to convert from a standard double and they can be used with nine or ten speed drive trains. The cranks are available in 170, 172.5 and 175mm crank lengths and will work with both Shimano and Campagnolo drive trains. The new chain ring combination also eliminates the need for cassettes like a 13x29 or 12x32, which tend to have large gaps in the mid range. And finally, did I mention that they cost much less than converting to a triple?