Listen carefully....you want to look at the Carbon Express Thunderstorm SE. It is a 600 spine, 30-50# rated. They were marketed as a kids/womans arrow, but are selling much more to trad shooters. Along with the light spine, they have a fairly heave GPI (8.3 graains per inch, I think). Any way, from my 48@27" BW, the tuned perfectly cut to 28 1/4" with a 125 gr point. Total arrow weight with my crown dip/creastin is 396 gr.
These shafts have a neet spider web pattern on them and go really nice with my Widows! They definately are much lighter spined than the GT's.
Give them a look, I think you will like them.