IMO it's a bit rushed for 6 days and, depending on what you enjoy or like to do, I would advise sticking closer to the coast. It's a 1,700 KM r/t drive between Vancouver and Banff, and about 300 KM extra for either of the alternate returns.

Driving in the south is fairly slow due to almost-exclusively single-lane roads. It'll take a lot longer to travel than what you expect (I'd say averaging 80 KM/h is pushing it).

I'd change the 1st overnight to Revelstoke instead of Kamloops if Banff is set. Well worth the extra 2-3 hr driving time (216 KM) on the 1st day and it's also more scenic and gives you more time to stop on the way to Banff.

The alternate of going north to Jasper, then south to Kamloops and Vancouver would be good too.