.357 Magnum is an eminently shootable round, especially in a large steel revolver. A 6" 686 certainly belongs in the "large" category. 1200 fps may not be a doughnut-maker (in the muzzle blast), but it represents twice the muzzle energy compared to a standard .38 SPL in the same revolver. If you want pain, switch to .44 Magnum (or .50 SWM). Even .38 SPL is a pain in a 15 oz J-frame. In a 42-48 oz revolver, NOT.

Muzzle velocity is elusive if all you have are loading specifications. You need to know what test fixture was used, which is typically a 8" or longer barrel with a closed breech. If you want to know, rather than interpolate your own performance, use a chronograph.

Reloading tables don't represent the edge of the envelope. There are too many variables to do that without extensive testing and quality control. Be happy and safe. If you want the ultimate performance, look to Buffalo Bore or other heavy hunting ammunition. Not all BB ammunition is safe for a Smith revolver, so read the label. For most of us, Federal or other standard brands provide a cheap, safe thrill at 1300+ fps from a 6" barrel.