Sorry for the late reply. I've been busy recently and didn't read the review section. If I don't respond some other time, drop me a PM as a reminder.
The HW100 AT is very difficult to deal with unless you have access to a workshop and are prepared to risk causing some damage to the gun.
To reduce the power by 0.5-1.0ftlb is not usually a problem on the AT guns. Rasing power might cause a steep power curve.
On the AT guns, dropping the power won't improve the shot count.
As you rightly said, you need full access to the internals (removal of AT) to set the hammer and reg properly and optimise the performance. With mine, after much experimenting, tweaking, a little poishing - and of course the removal of AT, I have managed to get around 95-100 per fill (11.4ftlb) from my two .177cal HW100K's.
As you have found, some HW100's can run below 90bar. There is quite a lot of variation in the way they are set up. Although I have not tried other regulated guns, I presume that other reg'd guns also have some variation in optimum fill pressure. If I remember right, Daystate guns have an individual data sheet for each gun's fill pressure.
I have one HW100 that fills to 180 and runs down to 70. My modified one's can work from 210/220 down to 70/80 and would give well over 100 good shots per fill if run between 220-70 (I'd guess 120 per fill?), but I try to stay within normal pressure ranges.