I'm no high range guy, but am working on a technique with tongue arch where I control the flow/velocity at the top of my mouth which so far is allowing me fairly well controlled sound up to about G above C over the staff. I'm still developing this - it takes a little mental preparation to adjust to it but when I do it seems easy and I'm keeping the pressure off. Some days though it doesn't "lock in" - but it's early days yet.
Now I'm pursuing just one method which seems to work for me -- without resetting chops I can play back in the staff, then get back up high again. I relate this only to indicate that you need never stop learning or developing. I played up to "high C" tops on my regular mouthpiece for 30 years before I started trying to play above that.
I used to use a Jet-Tone T3D mouthpiece with a lot of pressure to play higher, and I could for very short amounts of time before my lips were shot, but that mouthpiece gave me a very harsh tone on the whole which didn't suit me so much.
P.S. wasn't there some warmly entertaining guy pushing his high range method/training posting to TM in the last few months?