I have mine as proportional simply because the fees are smaller, but payout should even out in the end. I don't think Mhash really matters so much on each as you just get paid for the work you do.
Also, with 54mhash, its going to take you a while to generate coins. With close to 800MHash, with current difficulty, I generate about .5 a day. With 54MHash, its going to take you quite some time and may actually cost you more in electricity than you generate in BTC.
I suggest checking this link out...http://bitcoinx.com/profit/
You can punch in a few numbers and see whether or not its worth doing.