Well, I've got a 204 manual high-top campervan, and it's quick, and good for overtaking, and poor for economy (32-33, driven 'briskly'). I bought it because it was available locally at a good price when I was after a suitable van for conversion.
If there had been a 102 manual at the same time, same spec, for a lower price, I would have bought it instead.
Having owned several T4s and T5s (all campers) over the years, and tested many others for magazines, I reckon the 102 5-speed is about the sweetest overall combination, with the nicest gearing, and gets nearly 40mpg - driven precisely the same way as the 204 - with the revs kept up in the band, and briskly.
To me, it's all in the gearing, and the one I really couldn't get on with was the T5 140 manual.
Why? Because it was so high geared it wouldn't pull in 6th below 75mph. At 80+, it really went like an express train. Brilliant for the autobahnen, useless over here, and thirsty, too.
No such problem with the 102, nor with the 204, as it's better geared, and SO powerful.
I was never offered an 84 to test, but if it were at all sluggish, and I owned it, I would have had it remapped to 102.
Remember when a 102 T4 2.5litre was just about the most powerful van on the road? All things are relative!