thanks Sidewinder - your explanation and the photos helped a lot
I'm thinking of going for the full 50mm with the hope that it will increase the seat height profile too just for aesthetics. I'm thinking of replacing the whole seat with a Ducati Monster seat with little or no bezel for a minimalist and clean street-fighter look - which is why I'm looking for as much gap between that rear wheel and the seat as I can get.
But I'm guessing that will definitely put the rear wheel on the ground with the centre stand up and I may have to get an extension made for the side stand.
I'm looking at replacing the front end with either a complete R6 / R1 front end (which will reduce the height too) or apparently a KTM SuperDuke 990 set of forks will fit and they're the same length (near as damnit) as the stock FZS 600 forks.
Dropping 1 tooth on the front and adding 4 on the rear too for a 'bit more pickup'
I got the Fazer for a cheap price so, while there are other bikes out there that might be more suited, as stock, to what I'm trying to achieve, it actually works out cheaper in the long run to just mod the Fazer - as long as I don't stuff-up the geometry and handling!