Generally speaking a deeper sidewall will give a slightly more comfortable ride just how noticeable is a another thing. You could run 275/50 x 20" which would probably be a better ride than 275/40 x 22" both are the same overall diameter, 275/45 x 21" some where in the middle I guess but still same overall diameter as the other two, personally the 21" would be my choice.

Cheers
Col

What Col says. For a given type of tyre, more sidewall = more cushioned ride. Also more sidewall = marginally lazier steering, but there is no way to ever really experience this in such a narrow size window. So, here it is:

I recently picked up a 2016 SDV6 HSE and it came with 22inch wheels.

A mate also has a 2016 SDV6 SE with the Red Brembo callipers. But it came with 20inch wheels.

Now he has upgraded to 22in the 20in wheels have ended up with me.

I want to use them when I go off-roading or tow long distance as I think they will be better.

But at least they fit.

I changed my tyres to 275x45-20 and the difference has been quite dramatic.
The ride quality has improved immensly and my speedo now reads spot on with my GPS speed which I dont mind.

the ride quality can also be attributed to the tyres... I went from Kumho to Pirelli Scorpians. Handling, noise level and wet performance has been outstanding so far and with 10,000 km on them there is so far no discernable wear.

I havent had time to fit my Brembo's yet as it has been super hectic for the last 6 months but over the Christmas break I should get them done... I even invested in a pressure bleeder (a cheaper one but better than nothing).