I'm looking to upgrade my lowish-end 10 speed Bontrager crankset that came stock on my LeMond. I'd prefer something a bit stiffer, better quality chain rings, and saving some weight would be welcomed, but isn't crucial. I also plan to keep it triple, since my drive train is setup that way, and I'm not ashamed to use the granny gear on the last half of a hilly century ride. Also assume 105 is the lowest group I'd go with.
1) What are the differences in the crank arms between 105, Ultegra and D.A.? (exclude rings)
2) What are the differences in rings between those?
3) Can the same external BB cups work interchangeably across those groups?
4) Can rings be used interchangeably across those groups?
I'm not opposed to buying used, eBay, or a non-standard setup (different ring sized etc.).