Thanks for the input.

I started this discussion because I have been using the 1522 3.7 oz e-glass and have had 2 dings that caused splits across the seams on 2 different boats. That tells me it's not robust enough.
Fiberglass supply calls 1521 a warp biased glass but doesn't say the same for 1522. I will ask them and post the answer regarding how much glass goes in each direction.

The Surfboard forums say that Hexcel 4521 was beveloped with 65 % of the glass in the warp direction. That would be what I want to lay across the grain on my next boat.

I don't care too much about longitudinal stiffness because of the monocoque qualities of the strip construction takes care of that.

This is mostly about avoiding expensive s-glass.