No matter the number of tests, though, the difference is only a millisecond or so, which is negligible as the size of the input increases or if the mapped function does nontrivial work.
However, I've also tried the non-tail-recursive fold on very large lists, and it doesn't appear to blow the stack. mzscheme probably does something to prevent this from happening, like allocating "stack" frames on the heap (a standard technique for implementing call/cc without stack-copying, and if your GC is good it's not much of a penalty). Given this, it seems more defensible that arc.arc's 'map1 et al are non-tail-recursive. I think I may change lib/util's foldr to use the OP's implementation.
