Thanks for the input blokes.
Not heard of the 52l 'rule' Mr Nuts, makes sense I guess, though these panniers have now been on two other bikes successfully (originally they came with a VFR, I kept them and used them on a Fazer 600) and being a tight @rse thought I'd test the water and see if others had fitted such big boxes to theirs.
It'd definitely be a case of 'Does my bum look big in these' if I did use them..
Having said all that, I only managed 800 miles last year and was spurred into action purely following a trip to the TT.
Thanks again.