Hi Clive
Well, you are thinking of moving from a Sorento to a Defender !!!
I had one for many years, then Discoverys now a Freelander 2 and I am a dedicated Land Rover fanatic. I would say that you will certainly know the difference if you buy one. It is noisy, draughty and some say uncomfortable especially on long journeys, however I find them quite comfy to drive, a bit upright like driving a bus. One thing you will notice is the clutch - ever driven a tractor !! My son has a 90 and a 110 and tows with both, but he like me is an afficianado. If you are into repairing / servicing your own cars then the LR Defenders are like meccano sets - big boys toys.
Don't let me put you off as it is a great tow-car, fuel consumption is not great and the 90 being a short wheelbase is a bit more bumpy but much better with a load on the towbar. I am of course more than a bit bias but it is one hell of a leap going from a Sorento to a LR90, maybe a step too far for you !
Regards
Alan