Spoke to the AME today and he confirms all that has been said on the medical side of things. There is no ban as such but it would sound warning bells.
I think Gengis has more valid points to note about the seat loadings etc. I believe there is also a paper work exercise which can increase the max all up weight of a PA28. The only difference appears to be a slight increase in the pref charts and always using 1 stage of flap for TO.
MJ