Dom's 205 XS has been very well maintained and it was in great condition for a car of its age. We had a quick run in each others cars to compare them and see how they were up to modest speeds (around 80mph). They were surprisingly different both in their internal layout and in the engines. This is a brief comparison of the two UK XS types.

INTERIOR
The seats are the same in all XSs as standard, the Stratos tweed sports seats with the stripes running vertically, as opposed to horizontally in the 1.6GTi seats. Dom had replaced the rear seat (not a split seat, mine isn't either though many XSs and GTs have a 50:50 split rear seat) with those from a 1.6GTi and has plans to do the front soon.
The boot was very mush the same, non-carpeted, with plastic liner and lock for the spare wheel. Most noticeable was the front layout. The door panels were very much the same, with the red stripe near the top, though didn't reach as far as the window. The dash layout was also very different.
The glovebox in the earlier (pre-88) XS is, in my opinion, a lot better as it is a rigid space with a pull down door at the front, like with most gloveboxes, as opposed to the newer XS glovebox coming open like a giant ashtray. Above the glovebox were two flat recessessed areas to place valuables, where the newer dash layout is more sloped. The newer glovebox isn't particularly roomy and secure.
The centre console has different heater controls, being in the slide switch style rather than round knobs. Below the stereo, instead of the small storage hole with lift-up door, there are cassette holders. The steering wheel, Dom had replaced with a GTi one, but did mention the original was larger than the one in my later spec XS.

ENGINE
The XY8 engine in Dom's car appeared very low down in the engine bay, mainly for the reason of the twin K&N bolt-on filters on the carbs. Fitting these allowed for the removal of the air intake system, of which the large black cylindrical filter box ran along near the front of the engine bay. The engine appeared a lot neater, though did look quite a bit older generally than the later TU3. The design of the two engines was extremely different, virtually everything was in different locations on both engines. The brake servo was on the other side too. The actual comparison of both engines can be seen on the engine page.

DRIVNG
First point to mention was handling of the two XSs couldn't really be compared as Dom's XS has been lowered and mine hasn't, so his took corners better, though he did say my XS handled well without lowering.
His engine had done 74k, mine was on 124k, though they both went similarly well. He needed quite a bit of choke to get the engine going well and mentioned it runs smoother after a thrashing. So we had a quick spin in each others cars (private car park for insurance reasons).
The accelerator required more effort to rev the engine, it was much less responsive than in mine, unless pushed hard. The engine sounded generally harder and coarser and made different whining noises which were aided by the sound of the K&Ns. I found the actual feel of pressing the accelerator similar to some diesel cars, but with much more powerful direct response and rapid rise to high revs in 1st gear.
One aspect of the car I found to hamper fast acceleration was gear change movement. This was dramatically different compared to my car. It reminded me of my old Fiesta (also a D reg). The gear movements were huge and the linkage felt a bit loose with a little trouble reaching certain gears at times. In 1st gear I hit the CD sticking out the head unit. In reverse, my hand was against the seat, which had been pushed fully back for my long legs! A quickshift conversion would really benefit in this example as the engine certainly does feel very strong. The clutch felt a bit stiffer, though this is liable to adjustment and some WD40...
The car sounded quite loud out on the road and definitely felt very strong with raw hard twin carb power. My XS felt a bit more refined in comparison and a bit smoother but didn't really feel as powerful as Dom's XS. It sounded more like a modern engine, cleaner sound, though K&Ns would probably change that. The twin choke kick could be felt at times to scream to high revs when flooring it, which gave some advantage. But generally the later engine gave cleaner acceleration which was also noticeably quieter.
Another thing to mention is top end. Dom mentioned he feared exceeding over about 95mph as the engine sounds like it'd pack in. My XS seems quite noisy at around 90-100mph though seems to acheive around 110mph without much problem. No doubt Dom's could exceed 100mph, though with any degree of engine noise, anyone would be inclined to hesitate. Keep it under the red and it's usually ok though I do actually know someone who killed an engine by trying for top end....