GS Custom HV 40g bullets with 28.5g (not 26g-misspoke earlier) of Benchmark shoots 3800 fps (3815 to be exact) in my FIL's 700SPS.
Your results may vary.
Think you can look, look, and look and at the most you will find 27.3 grains of Benchmark to be max you can find for the 40 grain bullet. If you decided to work up to that much powder be very careful. I get a snug bolt with 27grains in the summer so I have chosen 26.5 at a little over 3600fps. Newest Hornady manual only gives 26.4 for a max load.
The driving bands on the GS Custom bullets allow you to load to higher velocities. On their website, they have 3800fps as the velocity to load for with that bullet/powder combo.
Start less and work up applies to everything reloading.
Simply stating that 3800fps is obtainable with 40g bullets in the .223.
