First of all, the 850GLT is not a turbo, and although some few very early 240 Turbos had an attached "GLT" label, so did some few 240 non-turbos from the same years. Now that IS confusing.
You should definitely go for RWD ;) and a 240T to equal the agility of a modern FWD turbo, if and this is a big if, you can commit the resources and energy to getting it in top shape, running right. That can be a lot of work. It can also be a hell of a fast car that nothing much on the road can beat in the corners. (Not that I ever personally got into a stupid and dangerous road contest with an overly confident 850R maniac and watched him almost lose the rear end in the turn trying unsuccessfullly to pull away from the '85 244Ti. But I digress.)
I am sure I have not helped you but I will say that the 850 turbo might be an easier car to have fun with right now, if you do not want to put all the work into restoring an old 240T. Personally, I am putting the work into an '83 242Ti right now. 8 hours to paint the door jambs and underside of the hood and trunk and some seal areas. But it will be spectacular to look at and to drive.