You have to remember here that Marquez didn't first look nearly as effective above 140 as he has over the last year and a half or so. If he'd taken on Pacquiao at welterweight right after he was going life or death with Katsidis and Juan Diaz at 135, I think there's a good chance he wouldn't have been strong enough or had the punch to handle him the same way. Not to say it wouldn't have still been a hard fight, but it probably would've looked more like the 2nd(which I thought Manny won) than the 3rd at that time imo.
However, hate to say I'd put money on neither men having been clean fighters over the last few years, so the timing of their moving up in weight is almost a moot point imo. Bottom line is Marquez has Pacquiaos number but not the raw tools or athletecism, it's a coin toss every time assuming they both prepared the right way.
As an aside, does anyone think Marquez could've really performed on the same level that Pacquiao did against the "handpicked" opponents he took on during his tear up the weights? Aside from the corpse of De La Hoya, I think Marquez may well have lost to every single opponent Manny fought aside from him above lightweight.