hey radboy - we're overlapping forums now ;-)
if you're sold on the idea of a 500, look at some race results. I think you'll find that the EX consistently beats the GS. The GS has a more solid frame for sure, but it's down about 15hp, which is a lot when you're dealing with such low numbers. I mean, percentage-wise, the difference between 38 and 52 is a lot bigger than the difference between 100 and 117.
if you can afford an SV, there is no doubt in my mind that it will take you further, and keep you happier for a longer time. The initial cost may be a bit more, but the tire wear will only be marginally more expensive, and you'll end up with a much better machine.
think of the 500's as the honda civic of performance riding. People race them, but it's not what they're designed for...
the SV650 is more like a miata - still cheap, but a lot more performance oriented from the start. just a better base to build upon.