I just had an interesting opportunity to compare these combinations so wanted to give my opinion and hear if others also have an opinion.
My V90 T5 FWD R Design with Polestar was in the shop for a day and I was given a T6 as a loaner and have had the day with the T6 so can now compare. I did test drive the T6 before deciding on the T5 and then subsequently adding P* but a test drive is so limited that I don't think it allows a fair comparison. One caveat - while I occasionally like a spirited drive I'm by no means a speed racer and couldn't be one even if I wanted with the state of traffic around here.
When I test drove the T5 I was pleasantly surprised by the turbo lag - it was much less than I'd been expecting. And since Volvo chose to add the supercharger to make the T6, I assume partly to overcome the T5 turbo lag, I was even more surprised about this. The T5 did lack a little in the 2/3 gear range but adding Polestar had a definite positive impact on that (that's the extra mid level torque the P* adds I assume).
The T6 on the other hand. It somehow seemed a little 'cruder'. The engine noise was much more distinct no matter what Drive mode I was in. The lag from a start really didn't seem much better in the T6 and if it was it was only a tiny difference. Regarding noise, the T6 is significantly noisier to me and the noise it makes seems more noticeable - I guess a combination of the supercharger and turbo. My hearing isn't the greatest (especially in high frequencies) but this was noticeable. The T5 originally was definitely quieter (or maybe teh noise was just more pleasant) than the T6 and the addition of the Polestar to the T5 adds a nice little growl which is much more pleasant than the T6 and is till quieter. When the T6 was warming up there was a definite whine from the engine that wasn't present in the T5 (may be specific to the car, I don't know). It seems that the supercharger can be heard all the time as well as the turbo and obviously the T5 lacks the latter.
Regarding the 'feeling'. The T6 does have more 'grunt' in some conditions but comes at the expense of some refinement. The T6 in Comfort mode (I didn't try ECO) felt like the Dynamic mode in the T5, both of which rev too much and feel jerky to me. Dynamic in the T5 with P* is fun for a few minutes with the paddles but too much for daily driving so my Individual profile in the T5 has everything in Dynamic except the drive mode which I put in comfort. Dynamic in T6 is a little too much for me. The Polestar in the T5 adds that little extra to Comfort mode that makes it more nimble and fun, adds the extral low end torque that it lacks vs the T6 but without being too much (like dynamic is in both).
So overall, these after-the-fact extended test drives confirmed my choice of the T5 with Polestar. I really didn't want/need the T6 and wanted to save the difference in cost but for me I actually prefer the T5 with Polestar for everyday driving. So while I may be predisposed towards the T5 with P* (or else I'd be admitting I made the wrong choice) I thought I'd share my thoughts. I'm sure others will think differently and that's OK.