Well I said the decision (dithering?) might take a while... almost 3wks actually.
Went for the Palm Hydro in the end from
Palm Hydro PFD - Red - With free Hydration Bladder! - Marine Warehouse Ltd from Marine Warehouse who were offering it at £79-99 inc a free £13 hydration bladder.
I should have been a M/L but sixth sense made me order that and an XL/XXL which was the next size up. Only stood to lose the postage when returning the one that didn't fit for a refund.
Despite me taking 42-44 jackets which should have brought me into the 43" capacity of the M/L I did need the larger size.
Each jacket has a certificate with its individual buoyancy rating marked and mine is a 79N. In a crisis the free 1.5l hydration bladder which fits into the back pouch can of course be used in reverse by inflating to gain an extra 9N... in theory!