Hi Troy
You commented that "Alot of images I have seen, not all taken by 35mm dslr's that are super macro lack sharp clarity". I'm interested to know just you would classify 'super macro' (as opposed to define as definitions so easily become contentious!)? Personally, I'd suggest that any image shot with a lens that exceeds 1:1 reproduction ratio is moving into the supermacro. And just a personal observation, but when trying out the Canon 60 EFS macro lens on my 1DS - to do so I have to use a 12mm MkII extension tube - it gives as good results as the camera is capable of utilising (and probably would do so on higher MPixel cameras too). If however I use the 25mm extension tube, there is a substantial fall off in image quality at closer reproduction ratios. I put this down to the fact that the lens is an internal focus designed lens and is optimised for a standard range (infinity to 1:1). In reality it performs very well at a slightly enhanced reproduction ratio but not when pushed much further.
Given the current trend towards internal focus lenses (am I right in thinking that Nikon's 60mm is the only smaller format lens which is not IF?) I suspect that we are already experiencing problems with newer type lenses lenses used for super macro underwater. I am assuming of course that your 'blad lens is either not IF or is optimised over substantial range - my experience with MF macros is limited to the old 'blad 6x6 135mm or more recently the Zeiss Contax 645 120mm which was an absolutely outstanding piece of glass. Intriguingly, I was recently reading up on the Leitz 100 apo macro and read at least one review which placed it squarely against the Canon 100mm - indicating that these lenses are now probably hitting design/manufacture/theoretical limits and are unlikely to be drastically improved.
So to get back to the reason for this post, I think that it is useful to understand the potential reasons for image quality limitations, and in the case of super macro these are alomost certainly due to use of 'converters, extension tubes, close-up lenses and so on being utilised with lenses the design parameters of which probably accepted a drop in quality outside of their 'standard' operating range.