Fatboy
You should by all means be able to obtain your velocity requirements, I doubt H1000 will get you their maybe Rutumbo or H870 or possibly wc872.
VVN 165
RL 19, 22, or 25
H4831, H4831 SC
Since you oviously shoot a lot you should have no problems nailing down what your barrel likes.
Now as far as longer barrels go, if you got it heavy fluted and added 2 inches, say .75 at muzzle tapered to within 4 to 5 inches in front of recoil lug/action face, for rechambering purposes a straight 4 to 5 inch section will allow you to get possibly 2 to 3 more chamberings out of the barrel.
Fluting
8 flute design, with four being .375 wide by .375 deep, and the other four being .25 wide by .25 deep, the .375 say start it at 2 inches from crown, and 2 inches from straight part of barrel at action end, the .25 flutes 2 inches from ends of .375 flutes.
Should look nice and drop a lot of weight but still give you enough stifness to lesson barrel harmonics.
I personally like Shilen barrels but since they onyl provide 32 in long barrels I only have one gun built with a Shilen barrel.
I think they are excellent quality and are amongst the top three competetors of benchrest comps so you cant go wrong, Lilja and Douglas would be my second and thrid respectfully.