As Ed pointed out, i have the Seikel Lift as well.
But mine is the Seikel Maxi HD which is for the T32 LWB and it uses Monroe instead of Bilsten.
I got a 30mm lift in the front and at the moment its sitting 60mm higher in the rear. (once the RIB, Battery and water tank are in, it should settle another 10mm)
I've been out on a few 4wd tracks, you really do notice the extra clearance, it handles heaps better off-road and on the tarmac.
I'm currently running Cargo Vector 2's and they are not bad
There is a 225/65 R17 BFG KO2 that is load rated, but i believe it isn't speed rated for you in the UK
That is about 4.5ish % increase in diameter from memory, i'm not sure on the brake loss at that % increase