For 6061 with carbide tooling go like a bandit; as fast as the machine can go.
With the qualification that if you have an unsupported length of bar in the spindle you might have to back off because it will whip inside the spindle and shake every thing; for short stubs don't worry just go crazy.
12L14 at 1000sfm sounds high; I think we generally run at around 500 or slower for turning and around 350 for parting.
I have to admit I have never done a good analysis of the best sfm for 12L14. It is possible that when you look at tool life in terms of number of parts per tool rather than tool life in hours, that 1000sfm is more productive. In other words the tools do not last as many minutes/hours but they do turn out more parts. Our machines run 12L14 barstock un-attended so we tend to be conservative on sfm to avoid catastrophic failures that wipe out multipe holders.
I just re-read your post:
.02" per rev feed???? Yikes that is pushing it for a little baby; I rarely go above 0.01" on my TL2 and on the GT20s we rarely go above 0.005. You are almost cutting a thread at 0.02".
Similarly the 0.013" for 12L14 is very optimistic; maybe if you had a whole flock of horses working for you but I think you are going to redline the spindle load meter.