And then they were four!
I have just acquired a Peugeot Optimum as well. One of the metallic Lilac Reynolds 531 frame versions. It has the standard RX100 gearset although mine has RSX100 Sti levers on it. I don't know if they were an after market addition or if it had them from new but it also has a different stem and handlebars, not the cinelli version but a generic Peugeot branded grey painted set with matching seat stem (which I have swapped for a Condor carbon one). Like you guys, I have struggled to find much info about it but I have found a 1992 Dutch catalogue which shows the Optimum model to be the 3rd of a set of top range models, although in their case the optimum is made with Reynolds 525 and the very top model is made with 531 and had Sti shifters so maybe the UK versions were not quite the same. My frame appears to be a 1992 model based on the code stamp on the bottom bracket.
It is a really nice ride. I have never liked allu frames, I find they transfer alot of road buzz and vibration compared to steel.
I had a Peugeot bike as a teenager and of course although it started off as a wonderful, pristine racer, as teenagedom progressed, it went through several resprays in a variety of two and three tone combinations and ended up matt black with the biggest set of cowhorns you have ever seen. I don't actually know what happened to it in the end although I suspect I out grew it, in every sense of the phrase.
I will keep looking out for info and if anyone else comes across any more details I'd be interested to know.