Yes, races are the best indicators of fitness followed by time trials. TTing a 1200 is a good way to estimate current miling potential, although you probably won't be really able to understand your 1200 times unless you've run 1200s before. In Sub 4:00, the book about Webb at Michigan, he time trials a 2:51 or 2:52 and then only runs 3:44 or so for 1500, but I think that is a freak example. I know if I could even run 2:55 I could probably run 3:59.
Traditionally, the standards are:
400: 52
800: 1:52
Races distances above the mile are not used much because it's more important to have the speed when you're talking about running 4 laps in under 60 seconds each.
Jeff See split 1:49 and ran 1:50 in an open 800 in HS (yeah, I know, high schoolers are bad examples), but only ran 4:04. Adam Goucher ran 1:50 and also ran 3:56.
Overall your speed is what sets the limits to your potential for the distances of 1 mile and down. 100mpw will help you for nearly any event, but if you can't run one lap in 52 seconds, you probably will never be able to run 4 consecutively in <60.