The K-H calipers are technically superior, but are they really an option? You can't buy the parts new. You can buy rebuilt calipers and new rotors, but also need the special spindles and hubs. The rare rusty ones that show up on ebay command high $$$. A member here has offered nicely rebuilt setups, but at high price (~$750) and don't know if he can even scrounge parts anymore. For the same price, you can buy a Wilwood setup w/ 4-piston fixed calipers.
Re SBP, you can now buy new 17" alloy wheels in SBP, so you aren't limited in any way.
Re DOT 5, I have run it in several cars for decades and have not seen a spot of internal rust since. If water drops got in the system they would not be absorbed and could theoretically cause rust depending on where they settle. Don't let water drip into your reservoir, which is true for any brake system. Fill it carefully and don't touch it, and you will never have to fuss with it again. I have newer MC reservoirs with tight-fitting plastic caps on all my cars, so no concerns.
