Re: 300 Tejas
I believe the velocity, my 338 Lapua Improved gets 3000 fps with a 300 grain bullet easily. I attribute this to the 32" barrel and the 5C Broughton rifling.
If you opened the case to 375, it would have similar capacity to the 375 Tejas, I see no reason it couldn't drive a 50 grain heavier bullet the same speed.
My load is 100 grains Retumbo under a 300 grain bullet, at 2975 fps. I have went to 104 grains of powder with no pressure, velocity for this must be nearing 3100 fps, although I did not have a chronograph when I worked up to a max load, which was never reached because of compression.