re: Tradehill - this sort of amount would probably be done in a dark pool so the (public) volume is irrelevant.
So you're saying you can do secret deals with Tradehill but not with Gox? A few percent in these terms is actually big money. 10% more USD for your btc on Gox = 100k. If you are a big withrawler Tux might take 3% = 30k which is not bad for 20mins of form filling/online banking and maybe a few phone calls.
You now have 70kUSD more than on any other exchange. No risk.