What would be the right form of to be in the examples below?
Five miles [is/are] a long way to walk.
Preliminary results [is/are] better than no results at all.
Use standard plural construction with "results are". Use standard singular construction with "is a long ... walk". "A preliminary result is" also standard usage. "The five miles are fraught with danger" uses plural, because the sentence does not cast the total distance into a single unit.