A couple of points.
First, what one can do with CFS is variable. In the section on pacing in Myhill's old free downloadable book, she put professional athletes who could no longer perform at their usual level at the higher functioning end of CFS. I was not an athlete but I came from a point where I was walking/hiking 50-75km a week. In my first year of CFS, 2003, I would walk 10km or so and then crash for two or three days and then do it again. I had not got the memo about pacing. My diagnosing doctor had no trouble recognising this as CFS.
(BTW My mental fatigue was much worse than my physical fatigue. I did a QEEG about 8 months in and was told that the noise was swamping the signal. I had major issues with aphasia, could not smell or taste and had trouble controlling my muscles etc. I also had chronic migraine and it was hard for me to separate out a lot of the symptoms, it was not until I came to this forum that I discovered that my issues with noise and light could be CFS symptoms too, I always though they were from the migraines.)
Second, re cmt12, is that in my case, pain is not the issue. I have pain of course, but I can easily push myself too far, to the point where a muscle fails or starts shaking, for example, without feeling any increase in pain.
And I am finding my attempts at pacing really difficult. Over the last three months I have been trying to be smart about this, I have been doing bodyscan meditations and had hoped that that sort of awareness of my body would help me work out when to stop. But last Sunday, for example, I walked down to the markets and bought fruits and vegetables and walked back (2.8km). This has been the big activity of each fortnight since December (when I had a completely unexplained improvement) and I had managed to do this for 5 of the previous 6 markets with no real problems (on the sixth I could not manage it and got lifts both ways). On Sunday I felt good walking to the markets and only needed six or seven short rests on the way home, and I felt good when I got home. The rests were just pauses really, a few second of standing still before continuing up the hill, and are a normal part of the round trip I did not see them as some sort of omen. Then I pretty much just crashed, I was wrecked for most of the day and by 10 am monday I was feverish, fluish etc and I am only starting to feel better today (Thursday). There was no pain, and certainly no fear of pain, there was just a collapse.
I don't know about Jeff_W's idea about creating a surplus. It sound's wise. But to stop before your warning signs arrived you would have to have predictable levels of energy, and I cannot see any patterns yet. I seem to vary too much from week to week. And I also have that problem of needing to do more than I can do much of the time. Hope it works for you though Jeff.