I have read about at least three different versions of a 6.5STW but have never seen one in person. It's the 7mmSTW (the 8mmRemMag necked down to 7mm) necked down for .264 bullets.
Google turned up this page of one guy's version with a bit of load data. No info on reamers though.
Personally, I'd pick a different twist rate than what was used so it would work with heavier bullets too...but if you want a .264 1000-yd prairie dog rifle it sounds like the hot ticket.
In fact, I have seen a .257STW...about the same as necking it down to .264, it would also be a limited life barrel.
Another parent case that would be a similar or even larger capacity would be the .300 Remington Ultra Mag. There is a version called the .264 Ultracat.
The 7mm and .300 RUMs are a ridiculously inefficient pair based on the .404 Jeffery case. It would be mildly worse squeezed down to .264 or .257...but if it's already that far overbore in 7mm then what's another couple percentage points less efficiency right?
Do you have a copy of Ken Howell's "Designing and Forming Custom Cartridges for Rifles and Handguns"? You could get lost in that book for a long time. He does a good job of explaining the science of and his personal theories on wildcatting.
Like Gibbs, O'neil, Ackley, Neider and all the other "old-timers", Howell puts the ideas down on paper pretty well and is must-have reading material.