Worried about losing the ride quality

[Greekthang]

Well guys I have a 2004 X4 4.4L and I just recently bought Breyton Spirits 21"

Now the only tire I can find up here in Canada is the Dunlop RFT. I was just wondering what the ride quality would because a few shops have said the ride quality is so rough and I will lose that ride comfort in my X. I also have on order H&R springs 1.5 lowering all around. Any with a similar set up that can shed some light on this issue. The roads are pretty bad up here due to the winters and I am afraid with the run flats being super stiff they could warp a rim.

The tire size I looking at is 325/30/21 in the rears and 285/35/21 in the front

Thanks in advance