[dsraven]

I would say you should always try to get the best "base" you can afford because it is a bit of work to get the diff under there and all hooked up and operational. if you go with too light duty then it may work for you for awhile, or forever, but if you decide later to do something different and the diff won't handle it then you do the hunt and swap all over again.
when i set up my first 57 frame I went with an A10 axle and got it mocked up. I found it was not going to work for me plus I was worried about the possible swap to bigger power at a letr date. then I went with a camaro 10 bolt, found it to be basically the same as the S10 plus it was too wide for my plans. I ended up with the ford 8.8 because the 9" ford stuff was either wore out or waaay too much for my build budget. I ended up with the ford 8.8 because it is relatively easy to find and that makes it cheaper and easier to find something good at the pick n pull yard. parts are readily available if you want to freshen it up before final assembly. it is a pretty tough axle that comes with the ratio I wanted, 3.73, and also has a posi, large axles, disc brakes with an easy hook up for park brake. I know it will take a hammering and keep going. a friend of mine had big hp in a mustang with this diff and he did nothing to the diff other than a new reinforced diff cover. I had my truck set up for a 4.8l LS engine but knew if I changed my mind I could put big power to the 8.8 and if I did end up having trouble there are a few racer tricks that could be done without swapping the housing and starting all over. the ford pattern axles were easy to change over to the chevy pattern with chevy sized wheel studs drilled into the axle flange between the ford studs so it was easy to match the mustangII front end with the small chevy pattern that the frame has.
so, end of the day, go with the best you can afford but try to build in longevity and upgrade ability. I always say "get the base right and build off that".

just my thoughts though.