To answer several of the proposed questions:
No, the 6.5x284 case length is not 284mm. It is named as such due to the fact that its parent case is the .284 Winchester, with the measurement of ".284" coming from the bullet diameter in inches. The Norma is labelled as such as a throwback to its parent case. By the way, a case length of 284mm would be 4.5 times the length of a .30-06 case, or about 2.8 times the length of the .50 caliber BMG shell. Imagine shooting something like that. Velocities of a 6.5mm bullet leaving that case would probably be in the 25,000 fps range, although there is a high chance that the bullet would vaporize the instant it left the barrel.
Second, the .300 WSM case is not based on the .308 case. If you put a .30 caliber .300 WSM bullet in a .308 case, you have what you started with- a .308. Same size bullets. The WSM case is a bit longer and CONSIDERABLY wider to allow for the extra powder charge to maintain the .300 WM ballistics. The reason that the ballistics are maintained is that the WSM case is also a bit wider than the .300 WM case, and utilizes a more efficient powder and powder burn column. Despite its short size, the .300 WSM still packs a bit of recoil, feeling only slightly lighter than a full-size .300 WM, due to the fact that it is usually chambered in lighter guns.
The .300 WM case is in no way based on the .30-06 case. To begin with, the .30-06 predates the .300 Winchester Magnum by several decades. The .300 WM case is slightly longer and much wider, with a proportion ratio similar to the aforementioned .308/.300WSM comparison.
Recoil of the .300WSM is a bit more than twice that of a standard .308. Ballsitics and ability to hold course through wind and other variables is drastically improved over the .308, as is retained muzzle energy and velocity at long range. It is a far more powerful cartridge than both the .308 and .30-06, and roughly equivalent to the highly regarded .300 Winchester magnum.
The only things the .300WSM/.308's and the .300WM/.30-06's have are relative heights and action length.
Sorry if I was redundant, but hopefully this cleared up any confusion or questions.