How about a 6.5-06 or 6.5-06ai. The 6.5-06 will give 200ft/sec over a 6.5-284 according to the 8th edition Hornady Reloading manual and the ai will give another 100-200 on top of that, both with the 129gr bullet. Cases can be made easily from 270 or 25-06 or A-square make them as a standard case.