I've found Pro400h to be spot-on on box speed. I spotmeter my subjects so I can't be that much off. However I've found it's prone not to be so forgiving on overexposures as most color negatives are. For underexposing is more forgiving. Meaning you can burn out some highlights when you shoot at some ASA100 or so, but this can also depend how you develop it.
It's a lot due to scanning and inverting technique used on the particualr C41 scan. If you don't know how to properly scan C41 negative then the results are almost always dissapointing, whether exposure- and colour-wise, or both, IMHO at least.
Pro400h is my overall favourite C41 film and I always shoot it right at the box speed, couple of my drumscans for "box-speed" (ASA400) proof:
David+Sandra by tsiklonaut, on Flickr
Gamelan man by tsiklonaut, on Flickr