I have the 5 foot version (RB60) and I have been very happy with it. I use it primarily for snow removal. I was looking at new too but then I was able to score a good deal on Craigslist on a used one. You might want to check around for a used one.
I have the 6' that I use with a JD 855 (24 HP) and it works fine. Even with a good blade angle to create a wind row it still covers my tracks and I have adequate power and traction for most jobs.
I use it to smooth gravel on a driveway. Getting a flat smooth finish can be hard. Pushing backwards works better than pulling forward. Back-dragging with the loader also works well. I don't have gauge wheels but they sound like they would be good for this application.
I angled it to cut deeper on one side and created a drain swale. It worked well for that.
I have an RB72 for my TC18. I also have the end plates and skid shoes for it. I use it to plow snow with and to help burn brush. These are really nice blades, buy one! New or used you won't go wrong.
You won't regret it. Built like a tank and thats what you need considering the rough use it will no doubt get. I fabbed gauge wheels on mine for snow removal.