Hi all, just following up on this.
I've had some fun this afternoon installing the shelving but I think it's a good result in the end. Obviously time will tell if the setup is manly enough, but it seems pretty strong.
I went with the GeeFix kit in the end as lots of people reckoned this was the strongest. I ended up using a combination of the GeeFix, Fischer DuoPowers, and actually managed to reach a stud for two of the shelves, as there was a stud I didn't realise was in a reachable position (anticipating told ya so's
).
The GeeFix looks like this:
You stick the long bit through the 25mm (I used 24mm which was good) hole in the plasterboard and keep the round cap on your side, then pull the red cord to align the fitting horizontally. Then while pulling tight, you screw through the centre. Then you remove the red cord and screw the fitting into the plastic etc. (terrible instructions but there are YT vids).
Stud found! One side only but still...
This bracket has, from left to right, wood screw to stud to the left of hole (hence wonky), Fischer DuoPower into plasterboard, and GeeFix fitting! Three different types in one bracket
End result: