Steve Porter,
I think if you would slow down and look at some case capacities and cartridge drawings, you would see that the case you need is the RSAUM. It holds ~71 grains of H2O as opposed to the WSM which holds 82 grains. The RSAUM case is 2.035", similar to the .308 Win. When loaded with the 143 ELD-X, you have room to make 3,100 fps if you so desire. Otherwise, you can use H-1000 as a cooler burning powder for lower pressure and less velocity.
6.5 RSAUM brass is available as 6.5 GAP 4S from GA Precision and their distributors. No wildcatting brass and there's a ton of reloading information, which is especially necessary if the ELD-X doesn't want to perform in your rifle. If you want another brass maker, you can simply neck down 7mm RSAUM to 6.5mm in one move with the sizing die.