It's been a while since I got my rear shocks and springs (illness/too long a story), but I put them on yesterday and today. One side a day's enough for an old crock like me.
The difference is absolutely night and day. The unladen height is now 400mm - before, it was around 360/365, so a good 35mm gained.
The car used to make a kind of chirrup or squeak, but doesn't any more. Also, going over speed bumps near where I live - the wide sort, about 8ft wide, not the abrupt rubber-like ones - the car now doesn't squat down on reaching the normal road again.
Interestingly the springs supplied with the car were 1K0511115BL - White/Green/Green dots. New they were supposed to measure 365mm, but mine were at about 345 after I took them off. Explains a lot about the sag, I guess. Also, it does indeed seem like they are weight range 6, not 10, judging by the car being a confirmed 1JA, and everything else on the car being standard - i.e. no rough road, no factory tow bar (I fitted mine myself not so long back).
So I'd like to say thanks to everyone who shared their info and expertise on here - special mention to @DrCorbyLee, but also @chimaera and @Carlston.
I haven't had the bike rack on yet - which is really what prompted doing this - but I'm pretty sure the added height and lack of wallow will help with that.
Should have done it years ago 🙄
Briskoda rocks!