Theoretically it shouldn't make any difference at all. However I cannot vouch for potential losses in a massive mining farm setup designed to channel PH hashrates through only a few workers. While I've personally written a proxy (and am still actively developing it to be something much bigger) I can't vouch for the proxies anyone else uses. This is nothing to do with whether it's rental or otherwise. My gut feeling is a massive farm (>1PH) is less likely to be as efficient and have the same amount of potential hash loss as a medium sized farm. It's hard to set up a good farm and the larger the farm, the harder it is - but it's not a given that whoever set it up won't have made it as efficient, it's only generic advice. As I've already said, no one with >1PH has ever found a block on this pool (except for the private Avalon farm that was mining here when I first opened the pool) whereas there have been heaps of blocks solved from 1->600TH miners.