Quite few differences - none of them on their own are monumental but add up to a better package on 850R.

T5-R, 30 secs overboost, interior was leather facings with Ameretta (no, not Alcantara) trim. Ameretta is stiffer and more "cardboard like". Motronic is different, and was built 94-95 available initially in yellow but 95 model year added black and an even smaller run of dark metallic olive green in 96 model year (manufacturing year 95). No other colours available as they went to TWR in UK for finishing in batches. 5 spoke "Titan" alloys (Suspectable to bending rims on really bad roads).

850R has unlimited "overboost", i.e. diff Motronic mapping, more torque, manual version got 10 hp more and more torque. Big improvement is addition of a viscous diff which helps traction and tyre wear. Suspension settings are slightly tweaked. Different boot spoiler (has a turned up lip in grey on the trailing edge). Interior is Alcantra seat facings with leather trim as mentioned by others. Alloys became 7 spoke "Volans" style. 850R is actually rarer due to short build run during 96 and the S70 model came out part way through 97. 850R assembled in house, hence the wide colour choice.

Most of this is evident looking at the two cars, the rest is gleaned from specs and a contact at TWR who actually worked on the suspension setup. He says go for an 850R if you have the choice (I did). For my .02c both are great, neither is a lemon even in yellow. Find a good one and enjoy.

I agree with John, however I thought there was a difference in engine spec. The T5-R used an overboost function limiting max power for short intervals. From memory (as poor as mine is) the power rating was 177kW. The 850R allowed this 'overboost' all the time. If you are in market for a manual, the 850R 5 speed offers a handfull of extra kWs at 185kW and extra 20Nm torque at 350Nm. The differences here are in the Motronic software.

Best thing about the T5-R? You can get that sexy yellow/grey effect model (if you're into that sort of thing). Ian Callum did a great job on

the T5-R design which still looks awesome today if in good condition.

The year it was made,that's it. The car was first termed "T-5R" for its first year or two but later just shortened to "R" instead. As far as I know, it's the same car.