Email me
V70s are cheaper but the 850s hold their value better. 99-00 years needs to be avoided. They're called b*stard years for a reason. 97 850 or 97-98 V70 would be better option. 94+ 850s and 97-98 V70s share the majority of parts too, if you need spares. V70s are slightly softer in terms of setup and handling when compared to the 850s, which are the better drivers car.
Cheaper V70Rs are probably manual swapped, which may or may not have been done properly, and probably a few issues. 850Rs are mental money, but T5s are cheaper with more parts availability and only differ from Rs in terms of boost pressure in terms of engine performance. Rs also sat 15mm lower from factory but you're no stranger to lowering cars. Aside from that it's purely cosmetic, and why I'd recommend T5s over Rs unless you're looking for a long term keeper/summer car.
T5Rs are rarer than the Rs and basically commanding the same price, and worth avoiding cos near impossible to find interior pieces for.
If you really want a wagon and don't mind crappy turning circle the P2 V70s (like your S60 T5) are probably a more sensible buy as parts availability both new and used is much better. They aren't quite as sharp handling wise but interior as I'm sure you know is exceedingly comfy, performance is on par (if not actually faster). If you don't want a wagon I'd go back to S60s. I love P80's and won't be getting rid of mine unless life forces me to, but they are getting to be a real pain to find parts for.