SUL73NAZ I am glad to see you're trying this out...will be watching your progress to see how it all goes for you.
The BTF arms will help since the uniballs are stronger than the OEM balljoints and do better with the increased angles.
Where you may see issues is situations where you droop out your suspension completely. Just when running BTF spacers you get spindle/coil spring contact in the front and CV/Frame contact in the rear. By adding the BTF uppers in the front that seems to eliminate the spindle/spring contact (your uniball cups on the arms may still touch the springs at full droop...this is not that big of a deal though....just reduces downtravel some). Obviously the that does nothing for the rear though. But as you said if you're not using your truck in a way that puts your suspension in that position it should be fine.
I've never fully determined it but I believe the rancho quicklifts (at least the front ones) achieve lift by having a design that moves up the lower spring seats on the struts compared to the OEM type strut design. This effectively makes the springs "longer" which causes the struts to stay a little more extended when the vehicle is sitting in the ground, resulting in added ride height. It also looks like the upper mount of the front quicklift struts is also taller than OEM-design struts. I had originally thought that this might be a thicker part that rancho uses. After thinking about it a bit it very well may be that in addition the higher spring seats, the front rancho struts are actually longer than OEM also, at least as far as the extended length.
The springs rancho uses (at least from the Electrician's experience) seem to settle a bit over time, taking away a bit from the achieved ride height. This may have been partly due to the fact that he has given those springs quite a workout on the dunes. Or it could be that the diameter of the spring coils seems to be a little smaller than OEM and they don't hold up to abuse as well. Hard to say. But regardless of this, the adjustable valving features of the quicklift struts are nice for customizing the ride characteristics so that is definitely a plus compared to OEM struts.
I've got a short work trip coming up but when I get back in November I'm going to be doing some experiments with modifying the OEM type struts in a way that will move up the spring seats (got some GREAT input and ideas from Duner on this). Should be pretty inexpensive. My hope is by modifying the OEM-type struts and using very short (1") BTF spacers is that I'll get a good amount of lift on the suspension (the same amount I have right now actually) but with absolutely no suspension components contacting the front springs and no axle/frame contact in the rear. If it works out I will do a writeup.
EDIT:
Here's what I was talking about with the Rancho struts vs OEM type. (Pics taken by the Electrician)
The front struts are here. Notice the difference in the positions of the spring seats between the two kinds and the height difference of the mounting plates at the top of the struts (disregard the Truxx spacer there when comparing):
And here are the rear ones compared to each other. The top mounts seem to be the same height here but the spring seat on the rancho strut appears to be higher than the OEM one, so the amount of lift in the rear is less than in the front when using the ranchos. This makes sense seeing as most people want to level things out when they lift:
