There were not cav at Marathon at all, neither Athenian of Persian.

redux, I assume you mean 600,000-700,000, yes? Personnally I find commas less confusing that full stops. Personnally I think 500,000 soldiers or there abouts seems more than big enough, Herodotus tells us that there were 98,200 Greek soldiers, including light troops but not, I think, cavalry. Given that neither side was willing to attack I would think the Persian Force was towards your upper limit.