I have gone with a T8 and so have my GF. But I would still emphasize some downsides - with the disclaimer that I am in the T8 camp - which, for some reason, I rarely see people mention.
- The additional weight is noticeable. The T6 is more agile, especially at low speeds. This seems to often be ignored in conversations. But every time I get a T6 loaner, my first impression is "wow - this thing can turn".
- I guess some people will dispute this - we have had endless threads here on the argument - but, in my opinion, the T8 is not as stable on snow. You can search around here. But I live in Buffalo NY now. I previously had one in Lugano, Switzerland. I drove to Colorado many times because I have a place over there as well. What I am trying to say is - I have a lot of miles on snow, and many of those on mountains. The T8 behaves well, but you have to keep in "constant AWD" mode (with my 2017 that was a pain, because I had to get gas every 150 miles in constant AWD... consumption was stupid). Hybrid mode is a no-no on snow. For as smooth as that transition is, it can fishtail you easily, when the gas engine kicks in at the wrong moment... that slight lurch is not ideal. And the rear bias at low speeds with the electric power kicking in is also not confidence inspiring. In power mode is does ok, but the T6 is still more sure-footed. And I want to emphasize - I am just comparing T6 and T8. The first time I drove my T8 in the snow I was far from disappointed. It does feel like it's on rails. Perhaps it is just a testament to the performance of the T6, that it does feel even more stable. Btw, the ultimate XC90 in the snow, in my humble opinion, is still a D5...
- My GF's 2021 T8 has a very loud electric engine. My 2017 was quiet. Volvo's regional rep's final statement, when testing the car was that "it is normal, the new electric engines are louder, noise cancellation is working, but I would not buy an electric vehicle because I find that sound unbearable". This is Volvo's one regional sales rep. Saying that "he would not buy" this car because, yes, the electric engine is bothersome. Truth is, that whistle can get bothersome, especially if driving in B mode. Most people won't notice. Frankly, I barely do. But my gf is younger and it bothers her. Her kids (13 and 16) flat out refuse to drive in the car, because it drives them nuts. Something to consider, I suppose. But it is the dirty little secret of electric cars. Most people don't have a problem with Tesla's. My father sold his immediately because it bugged him. Sound perception, especially at those high frequencies, can be very subjective, I suppose. In the 2021, I can barely "hear" the engine - but I can definitely "feel" it. The best way I can describe it is like a ringing in the ears. I used to suffer from hyper-tension. It's the same "ringing in the ears" you get with high blood pressure. I actually have 90% hearing in my left ear do to a scuba-diving accident - and I can't hear the electric at all. But I get that whistle when accelerating and pressure/ringing when in B mode.
I won't comment on the other issues... spare tire, fog lamps, leg room in the second row, etc.
All I am saying is... it's not a clear choice. I would not simply assume the T8 is a better vehicle.