Depending on the individual movie and the type of encoding selected, you might not notice any difference between the output from the two programs. Movies that require a lot of compression, and/or have a lot of action would benefit the most from the 2 pass encoding done by BD Rebuilder.
Speed of encoding depends quite a lot on the speed of your cpu and the number of cores available in the cpu. I've done backups to single layer BD-R, 25gb disks that took 10 1/2 hours using BD Rebuilder on two pass VBR encoding. That was on a quad core Intel processor, a Q9550 running overclocked to 3.4ghz. I also had 8gb ram, two 7200 rpm hdd's and used one drive for input the second for output.
Another movie that required little compression, I did with one pass ABR encoding and it took ~6 1/2 hrs to compress to fit a blank 25gb disk.