A lot of stuff being thrown around here. If you really need help with video editing workflow, try these websites/forums:
www.videohelp.com
www.doom9.org
Videohelp is a great place to start with a busy message board and is fairly tolerant of new posters. My go to place for help.
Doom9 is the geek board and while there is a lot of great, in-depth info, you hade better bring your 'A' game and don't deviate from forum guidelines. Bans are fast and frequent. Outside of the gaming sites that are populated by teens and mouthy young adults, it's the least friendly forum I've ever been to.
That being said:
x264 is the open source version of h264. h264 will also be called AVC on occasion. For the most part, h264/x264/AVC can be used interchangably. Encoding speeds using this codec can vary greatly depending on your material and/or settings. I can re encode a 2 hour DVD in 20 minutes or 8 hours depending on the settings I choose. The settings and the encoder are basically the same, regardless of the front end UI. Handbrake is the most popular free one and the one I use most. RipBot264 is another great free one that isn't quite as flexible, but has recently enabled distributed encoding which can be very useful if you're equipped.
Neither of these utilizes GPU encoding. The nVidia version is called CUDA and the AMD version is called OpenCL. Your software must be written to take advantage of it and it can make the jobs considerably faster at the expense of quality. As a general rule, GPU encoded video is inferior to CPU encoded video. If it's something you want to try, IMToo and Xilisoft give you the option to use CUDA/OpenCL. If you are a serious video editor and don't need to encode a 30 minute clip in as little time as humanly possible, then just stick with CPU encoding.
My CPU progression over the last few years looks like this:
AMD Dual Core 4400+
AMD Phenom II x4 955 and it was about twice as fast for h264.
AMD 6100 6-core is about 40% faster than the 955.
I would guess that a stock 2500k would be about the same for h264 as the 6100, maybe a little better.