2 BTC and up -always- requires confirmation [this is after hundreds of games], regardless of the fee attached. I know my 1 BTC bets used to get instant response when they had a fee attached, but I never made any between 1 and 2 to determine where the exact cutoff was.
It would be nice to have the old instantaneous SatoshiDice back, but I can certainly understand the need to wait for confirmations on large bets. It's just too easy to attempt a double spend when you lose, and on large bets, there is significant incentive to do so.
I'm thinking input confirmation is what's slowing things down. I did a test by moving BTC into a fresh wallet and using a mixer to get "clean" coins and initially even my larger bets (5btc+) seemed to return almost immediately. Over time they slowed back down to what I had been experiencing before. Hardly conclusive, but I do think perhaps shoving your results into a separate account and only betting with fully confirmed coin will always yield quicker return times.
The initial reason for the test was that blockchain.info kept losing network connectivity resulting in the "double spend" warning being applied to that wallet, so I wanted to see if there was any noticeable difference in win rates or round trip times after being "badged".