6.5mm bullets will do plenty fine on Texas game. I'd argue they are a bit overkill for most Texas game because of their velocity. A low-charged .30 caliber bullet would damage the animal less than a 3000+ FPS 6.5mm bullet, but with a precision rifle, you can just headshot the animal anyways.
I am looking at a .260 Remington Ackley Improved for my bolt-rifle build. It'll be barreled to accept 140+ gr. bullets which push the BC way beyond what you can get with a .30 caliber bullet in an acceptable load.
I agree, my friend shot a 180lb south Texas buck last year with a 55grn ballistic tip.. The deers legs went out from under it and it hit the ground hard. My other buddy shoots a thompson center .223.. same thing 55 grn ballistic tip. he takes neck shots at 100 yards.. He has never had a deer run away from him.. Its all about shot placement in my opinion but a good bullet also helps .
I think I just purchased another 300 wsm.. I just found a win mod 70 for $300.00 .. and i had to buy it.. looks like I have a new deer gun for next season...