I want to change the crank arm length on my Bianchi 928 CF bike. The current set up is FSA ISIS drive Double Compact.

I have no problems with the BB or the FSA Compact and have located a crankset of the length I want in ISIS at a good price so I'm inclined to buy them and I'll have a spare set of chainrings for future use.

My concerns are:

Mega Exo and other external bearing BB set seem to be more prevalent, the current choice. Is ISIS drive on the way to obsolescence (at least sooner than the external bearing BBs) and will it be hard to find in oh, say, five years when it may be time to replace it?

I think I may want to have the BB shell faced before I install this hypothetical BB. What is a fair price to pay for this? This needs to be factored in to my budget.

I am not a sprinter so the stiffness I hear about with the Mega Exo is probably not a a big deal to me. Durability is. Is there a difference in usable life between the BBs? Is the external bearing easier to service?

Thanks!