Just experiment for yourself. I wouldn't suggest back-dragging a bucket on anything other than loose soil. You certainly don't want to be trying to cut hard dirt with it. That's a good way to burst hose and wear on the bucket edge, possibly bend it as well.
The more down facing angle on the bucket when dragging back will allow a more aggresive bite into loose dirt than with the bucket flat. If you're just smoothing out dirt, place the lift into float and add just enough down tilt (dump) on the bucket until you see the rear of the bucket lift slightly.
The smoothing operation is rather handy if you're digging a hole with the FEL, every 4th or 5th time going in to fill the bucket, just do a float drag back on it will help keep the ground on which you travel, smooth. It's pretty much required if you go in for a full bucket and get wheel spin causing the tires to dig up your travel area.
Also perform said smoothing operation if you're continually driving over your tracks like accessing a pile of rock or moving a dirt pile.
For moving the amount of dirt that you need to, the box blade will be the most cost effective route, and you're likely to find a few used ones on craigslist. The best part about buying a decent CL item is that you can get some use out of it and then sell it for what you paid. As I stated in another post, I just purchased a 6ft box blade and 6ft 'rock' rake in excellent shape for a total of $800
