Topshot, I have been thinking about this same question.
I lean to the 7mm RUM or a 7mm-338 Lapua wildcat.
The 7 RUM is the most potent legit (non-wildcat) load available. You can get the Sendero out of the box and they are supposed to be quite accurate that way. With a little fine tuning like a trigger, some skim bedding, custom dies, it could possibly match some customs in accuracy. After the barrel is burnt out, a custom could be fitted to it along with blueprinting the action, etc. The only available brass that I know of would be from remmington or getting some Nosler in 300 RUM and necking down. The Nosler would probably be better brass and costs about $56 per 50 I believe.
With the 7mm-338 Lapua, the advantage here would be the availability of Lapua brass. I think it would have slightly less case capaciity than the RUM so probably a little less velocity, but more than the Dakota or STW. You could also work with your smith and modify/improve it slightly to boost the performance a little. I think this would be working in the direction of the 7 AM? The other advantage would be that this would be a custom or partial custom, depending on the components you use. I would think you would want to keep the reamer for custom dies and follow on barrrels. The disadvantage would be increased cost and waiting time.