Ok, I have been doing Minecraft videos in 1080p for well over a year now. Let me tell you what I have learned.
GPU and the RAM it has is central to FPS. If you want to have an FPS of at least 30 (the video will look bad if you don't) when using almost any modpacks, you will need at least 1GB of RAM in the video card and almost any processor that has been manufactured in the last year or so. 2GB of RAM is better, and will give you a very comfortable FPS.
You will also need a ton of HD space. I would record for an hour and fill up over 100GB of raw footage. This video should ALSO be saved on a different drive than where your Minecraft files are saved because that'll also slow you down with all the file I/O.
For best results I got a lot of RAM on my first recording computer, created a 4GB Ramdrive in it, loaded Minecraft into that (using Robocopy to copy the files every few minutes to a HD so a power loss wouldn't erase everything) so that Minecraft I/O was non-existent. If you can afford it, I'll recommend this to you.
Minecraft, itself, is severely CPU intensive. If you are recording AND playing the game, I suggest Xeon or some similar SERVER CPU, because you are going to be working the hell out of that thing. If you are uncomfortable building/repairing PCs, for the love of all that's holy do not try to build this yourself, one bad placement on the thermal paste and your CPU will be a brick (speaking from experience). I have only ever used Xeon processors.
When rendering 1080 video, it will take time. A higher GPU and RAM will make it go a HELL of a lot faster. If you have time, it's not a big issue. I just upgraded to an Alienware 14 and I can now render videos faster than it took me to record them (when previously it took 3x the time I took recording them to render them, on a similar machine with half the graphics RAM and GPU power).
SO, bottom line:
CPU is most important for GAMEPLAY. Server CPUs are more expensive, but can handle the workload easier. Last thing you want to do is lose the CPU from overuse.
GPU is is next important for GAMEPLAY and RENDERING. Better numbers = better FPS and render times.
HD is necessary because you are recording in HD, and multiple drive are really required if you aren't using a RAMdrive for storing the Minecraft files.
RAM is less important. Minecraft won't use more than 1GB, usually. Any OS usually won't use more than 1-2GB. Recording software uses even less than Minecraft. 4GB would be fine, but 8GB usually isn't an expensive upgrade and is helpful if you want to do other things while playing (like Skype/Nettalk).
Hope this helps. Welcome to the ever-expanding Minecraft YouTube recording community. T-shirts are being designed as we speak (not really).
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