Tom Van,
I seriously thought about building a 6.5 WSM about 2 years ago as my gunsmith had just made a brand new reamer and we were both dying to use it. But after having another hotrod shoot out it's throat, I decided to play it safe and just do a 6.5-.284. And man I am glad I did! After working with a 6.5-.284 for awhile now, at ranges from 500 yards to 1760 yards, I can say it was definetly the wise choice. Yeah, I gave up 200 fps to the WSM case, but at 1000 yards it really doesn't amount to much. You can get more vertical impact change from mirage than from 200 fps! The 6.5-.284 also burns way less powder which means you can practice more without your throat getting toasted, and in my mind that is way more important than shaving a couple inches off the trajectory.
As it turns out, I was talking to my gunsmith about the 6.5 WSM a few weeks ago, and he admitted that it wasn't the best cartridge. He built a few for some other guys, and they started shooting badly after only two seasons. They also said that it didn't shoot good unles loaded to the gills, and it had a tendency to heat up the barrels fast. Sounds like a high price to pay for a few inches.
Remember the old .264 Win mag? It has about the same capacity as the 6.5 WSM and it has been well documented by Winchester that when they were developing load data for it, it burned out the throats on 2 barrels before they had tested all the powders they wanted to try!
just my two cents! --goodgrouper