That is my old Rosso Trionfale at Dicky's. Great car and unique colour combination.
Had a GS and a GT.
In essence, the GS is more pointy and feels a lot older. GS handles better IMHO and the 300kg weight difference tells. I tended to drive the GS harder than the GT as it just seemed to demand it.
GT miles ahead in refinement, noise and every day usability. The weight tells if you are pushing on, but you tend to drive it less on the edge and relax into a rather fast but relaxed gait.
Cost-wise to run pretty similar.
So for regular use - the GT. There are also a lot more of them around and I think the parts situation will be much better in the next few years.