Phil L wrote:
Snip
Terry W.

As the others have said, you cannot get a good enough fixing on PB for
anything substantial.
You CAN get good fixings on the studs, providing you use good screws etc and
are careful that they are driven squarely in (in the centre of each stud to
avoid splitting)
As far as measurements of shelving etc go, these are dictated by the
studding - IE, if the studs are at 16 inch centres, the length of your
shelves have to be multiples of this, 16, 32, 48 etc, otherwise they will
sag at the ends.

Nonsense! Fixing onto plasterboard takes a lot more care and planning
than brick, but it can be done, even for heavy loads like rads,
cupboards, cooker hoods etc. Planning the fixing so that as many
fittings go into studs makes things easier as you say, but it's not
essential, and sods law dictates that the place you *really want to
hang the stuff* doesn't comply with position of the studs.

The type of shelving that the op is proposing should actually be
pretty easy, as the modular shelving rails usually allow fitting into
the walls at several points, spreading the load, and the long length of
the vertical rails minimises the moment force that would normally be
trying to pull the shelf support out of the wall. If you want to
absolutely maximise the load ability of the shelves you could leave
rails as long as possible so you can have more fixings into the p/b, or
even have the rails go to the skirting, although I doubt that is really
needed.