You should be able to bet about 176 BTC at 50% if the max profit is 176 BTC, since at 50% your profit is about the same as your stake.

SatoshiDice doesn't have the same max profit across all of its bets though for some reason, and never has done.  I don't know what the reasoning is.  Maybe they're willing to risk more than they can really afford (from a risk-of-ruin point of view) on the low-chance high-payout bets because you're unlikely to win many of them?