I have personally never heard of anyone using N540 in a .223 with 90s, but that in no way means it hasn't been tried. It falls in the appropriate burn rate range, so it might work. The only questions I would have about its use for this purpose would be the size of the kernels/bulk density and its temperature-sensitivity characteristics. I recently purchased a couple pounds (each) of two VV powders to try in my .223 Rem and .308 Win F-TR rifles as potential alternatives to H4895 and Varget. I haven't gotten around to any testing yet, but even if they just work "OK", I can always use such loads for practice, thereby saving the Hodgdon powders for use in matches. If they work better than "OK", I might end up switching powders due to availability. In any event, buying a pound to test shouldn't be wasted money. Powder Valley currently has one pounders in stock:
Discerning shooters reload their ammo with Vihtavuori N540 smokeless powder from Powder Valley. Vihtavuori powder is available in 1lb canisters and 8lb jugs.
www.powdervalley.com