The GT has a longer Stroke and Lower Compression, also a pretty decent size bore, the GTS has shorter stroke, higher compression, okay bore, the thing is, yeah the gt might get 50 and the gts might 40, but the gts still has more, but your forgetting one thing, the gt is ALOT torquier, and will have more tq, at less psi then the gts is still had more tq, so go figure. Gt is eaiser to customize, to make the GTS equal to the Gt, youd have to get a stroker kit, bore kit, and lower compression, all you have to do to the GT is lower compression, also, it comes stock with all these things, remember, cylinder sleeves to bore it out, arent always trustworthy, especailly with the already thin cylinder walls that the celis have!!
I'd say go with the GT, you'll have better gains, that higher cam lobe wont last a long time with the pressure of boost, GTs can handle 10-11 psi, easily, it be rsiky to go more than 8 for a gts even that is too high for daily driving!!!