When you backup a 43 gb movie to fit onto a (nominal) 25gb disk, you are doing far more than just ripping the movie. Compression of high definition material takes a lot of cpu speed, and your core2 duo running at 1.67ghz just isn't fast enough to do this any better.
For example, I used to use a Core2Duo dual core processor for high definition encoding. I would rip with AnyDVD HD to the hard drive, then work with the movie from there to speed up the process, but even with a dual core running at 2.7ghz, it would take 15 to 17 hours to process the movie. This was using BD-Rebuilder, 2 pass encoding, which is a good quality setting, but not the fastest it can go.
I'm now using a quad core 9550, overclocked to 3.4ghz, encoding from one hard drive to another, using 8gb of ram, and it still takes anywhere from 8 to 11 hrs to process a blu ray movie, depending on the size of the original.
Your problem isn't your blu ray drive, or your software choice. It is your hardware, specifically your cpu speed.