I've switched back and forth (power vs. speed) a couple of times (Ultra w/750c display, 5 PAS levels), but it's been a while now. I don't remember the PAS "dropping out", if that's what's actually going on, as a big deal? My throttle doesn't seem to be active at all (in either mode) unless the throttle power setting exceeds the amount of power being supplied by whatever PAS level I'm in. In other words, it acts like a PAS override. If I'm using the throttle (which is not often), it's generally to catch up with the wife or others, while crossing a road, or maybe for a little extra power for a short term "situation". Of course I generally ALWAYS use the throttle to get the bike moving from a stop, even if the bike only moves 18" until it's released. In any case, this doesn't change, or I haven't really noticed a change, no matter if it's "speed" or "power" mode I'm riding in.
I THOUGHT the power vs. speed modes were about how the controller handles PAS. In "power" mode, you assign a certain level of power (assist) to each PAS level, and your speed will have no affect on that amount of power, ever. If your situation requires more assist/power, you switch to a higher PAS level. If you're pedaling along and it feels like you are contributing nothing, or not enough, you switch to a lower PAS level to get less power (assist).
In "speed" mode, the amount of power available will taper off as you get to a certain speed. If you want to go faster than this speed, you need to increase to the next level of PAS. This leads, if I remember correctly, to the situation where it seems like no matter how hard you pedal, the bike goes no faster. You can back way off on the amount of effort you're contributing, and the bike doesn't slow...... HOWEVER, if you are riding within the speed limitations of the current PAS level, I think this mode may be smoother when it comes to torque sensing?
Does that make any sense? -Al