RE: light wind sail for original go
I think the Severne Glide is very powerful for a 7.5 m2, but I don't think it quite makes the same power as a 9.0 m2 Retro.
As much low wind go power as maybe an 8.5 m2 Retro, but not as much as a 9.0.
The German "Surf" magazine thought the Glide was nearly as powerful as some of the 9.0 m2 rigs that they were testing at the time, but that was a very subjective claim, and I don't think they were testing really powerful 9.0 m2's like the Retro.
Hope this helps,