for not complete info...
I take it from the back...I really am no North sails type (me personally, only severne).
More efficient in low winds is definetelly Glide (and I compared the same size, it means 8.5).
I weight 95kg (yeah a big boy)! Of course there are days where I could use something bigger (10sqm would be the max for me) but currently it is my biggest one.
About the wind range of element 8.5...I would say from steady 10 knots with some stronger gusts I can get it planning. When plannig the sails is very efficient and when you are calm on the ride it plans through luls nicely.
As the wind gets stronger my next choice is Severne NCX 7.0 (usually with another board...in this case Aero 117).
As for almost every Severne...the mast length for a certain size is a bit smaller and so is boom length (due to a droped clew), the sails feels a bit smaller what makes the ride more comfortable.
PS: S-Type 137, Element 8.5 is one of my favourite combos! Go for it!