"if you have a wide band, closed vs open loop is off the mark"
I'm not sure what you mean. Do you mean that a wideband system is always in closed loop?
"you should be monitoring the actual A/F ratio"
I am. But I'm wondering if open-loop mode ever happens, and how I can detect it happening.
"You will hit a point somewhere that the A/F ratio will begin to richen with increased throttle opening."
But I don't really "hit a point somewhere." What I notice is that AFR goes from lean to rich in a fairly smooth, linear manner, all the way from closed throttle to WOT.
"Keep that mixture as lean as possible."
That means using very gentle throttle settings. My experience is that this leads to pumping losses, and hurts FE. I suppose it would hurt even more if this engine did not have lean-burn.
"My suggestion would be a throttle stop"
You're suggesting the opposite of what I found, that large settings are generally preferable to small settings. That's reflected in my mpg results (and those of others who do well with P&G, I think), but I didn't grasp why until I read this:
http://www.autospeed.com.au/cms/A_110216/article.html
"I think P&G will be very hard on your driveline."
I think you'd be right if used WOT in the lower gears, but I don't. I'm mostly talking about low RPM in top gear. In my car, 2500 rpm in top gear means about 69 mph.
You'd also be right if I was causing pinging. But I'm not. Assuming a level road, I can be in top gear at about 25 mph (less than 1000 rpm), and use WOT to pull smoothly from there, with no pinging or lugging. My sense is that this motor is very happy to be driven this way. Periods of low revs alternating with periods of even lower revs (idling, or engine off).
I think I'm learning that low revs pay off, even when it means high throttle and rich mixture.