There are loads of sites that give detailed info in regards to actual encoding performance based on different CPU's. This site for instance

. Go to the main page and hit the Bench link. There choose Video Creation and encoding from the first drop down menu and then on the right plug in a few CPU's for comparison. If you are doing BR rips, choose the X264 comparison charts.
If you are sticking to the 775 platform then yes getting say a 9550 quad would give you a nice boost. Also depending on what software you are using, like say DVDFAB (yah you gotta pay for it), that program leverages your GPU (if supported), for decoding and encoding. If you have a relatively newer Nvidia based card that supports CUDA, you will see a massive gain in speed. Combine a quad with a CUDA based GPU and you would be amazed at the increase.
If on the other hand you use apps that do not take advantage of any sort of GPU acceleration, then at this point it's all CPU and the fastest/newest/most core'ish you can get will be the only solution.
Moving to a 2500k would be a massive jump especially in encoding (though I am not sure 100% if or what apps you would require that would levarge the new capabilities of the 2500K). However with the 2500K you would need to grab a new mobo and DDR3 RAM... so some cost there.
Edit: on a side note, if you are not worried about actual space on your storage system, you could also just "rip" the BR movie (main file) to your system. Takes WAY less time but again that is if you don't care to have 20-30GB movie files.