I need some advice on buying screws

2" x No.8 is my standard goto screw, with red rawlplugs. Might move to 2" No. 10 for a bit more beef.

Got through quite a few 3.5" x No 10s in the loft screwing down 45mm x 45mm battens

 

I did put a lot of caveats in and it's no good talking to me in Lbs.
Even if a wood screw is a quarter as strong, and I'm sure it's more, that's 175Kg per screw, it's not the screw that's going to fail.