It's not that my machine is bad, it's just not cutting edge anymore. I'm running an i5 rather than an i7, and minecraft actually runs worse on my computer than modern AAA titles.
I was getting a solid 100-120 fps in 1.6, which was halved when I moved to 1.7.
And the challenge is mostly fighting framerate stutter when I'm recording, so that's mostly extra cpu drain. Currently saving up for a major upgrade to my system, so it's perfectly fine if my base *eventually* gets laggy, as long as I manage to upgrade my computer first.
I'll just go for it anyway, most likely I'll be able to upgrade before it becomes an issue.