I'd get the 70x if it were me, as that's what I did. I see you're from the desert, so granted there are days when the atmosphere will not allow use at 70x, but when it does, 70x is still very sharp and detailed with no tunneling. Amazingly so actually. 20x on the low side give me all the FOV I'd ever want or need anyway.
I've had mine side by side with my Kowa 884, Zeiss 85 T FL many times, Swaro's 80HD, a Nikon 82ED, and a Vortex Razor 85 HD, though not all of these at the same time. The S2 proved superior to my eyeballs, so that's what I kept. The closest thing I've personally used that's close is the Kowa 884, but the image at max magnification sold me on the S2.
