I've got the same set up, bought my T6 from Leighton Vans with a set of 20" Axe wheels and 40mm drop.
It's my daily drive work vehicle and I got so fed up with speed tables and steep driveways I've done the following.......
I've since had the suspension changed to Koni adjustables but left the cobra springs on, less than a year later I've now got standard springs, standard Devonport wheels and tyres with Konis and the ride difference is incredible, 3 of the rear rings were together and doing nothing !
Once the weather gets better the 20s will be back on and I'll start saving for air ride.