Unless your into extreme offroading. A disco will do everything a 90 will do, and do it just as easily. I was in a very modded, lifted, 300TDi engined 90 this weekend and we had a completely standard 200tdi Disco in the group. It managed Gatescarth Pass better than the 90 did. The reason? The huge wheels on the 90 completely bollixed his turning circle. and Gatescarth is a very very twisty climb. we had to shunt most of the turns at least once and sometimes twice. While the disco managed every turn in one go. Don't get me wrong the 90 was an awesome machine and once the track straightened up it couldn't be faulted. But this was one circumstance where the disco was better than a 90.
And before you say owt else I've owned disco, 110, and 90's. So I'm not in the least bit biased towards any one vehicle