jim --

1592 beat me to it, so I'll just have to agree w/him --- that msw example is more about pace than 'class'.
I think pace is probably an occasional factor, but not so frequent or predictable as many would believe --- and of course, just my opinion.
the problem w/pace is that it's mostly an after the fact thing that's used to rationalize a result.
you don't really know if pace was a causal factor, but that's how it 'looked', so that's how it gets labeled.
I'd log that in the same diary along w/every other trainer excuse --- maybe the track was greasy.
for every example you come up w/as anecdotal evidence, I could produce a counterexample --- well, I could if my memory was better.
I think roses in may might be a good one, or the race that broke cigar's streak, if you want a high profile one w/a little dust on it.
I've seen countless lone speed's w/bad Sheets get swallowed up, and I've seen countless 'hotly contested pace' runners w/good Sheets keep running.
that said, I think it IS possible that the occasional horse gets burnt on a quick pace and quits, and in that case their final fig is just going to look like an x, and you need to keep in mind that it's a 'quit' fig.
you could maybe make a approx fig by shaving off the quit, or simply add a 'quit' notation, or just handicap w/that in mind.

as for 'class' I think roses is probably a good example, once again.
another would be a race I played quite a bit ago, where I liked this 25-1 horse --- the gappy drop down dutrow chalk was fastest, but the price looked better than the rest.
so, anyway, after he wins, these guys at the next table were lamenting that nobody could've played that one because he was the cheapest horse in the race.
I use a form, but not much, so I hadn't noticed, and neither had the horse.
(and so as not to pat myself on the back, while I did cash him, I blew the exacta and the double).
the problem you're going to have defending 'class' is that there's no definition for it --- you can't really quantify it.
it's about as meaningful as trying to come up w/a system based on how much 'heart' each horse has.
is roses now a classier horse than he was before his last race?