Last fall I shot a mulie doe at just under 200 yards with a 250gr SST behind the equiv. of approx 120 pelletized powder (105Gr of T7 loose). The bullet completely passed thru her rib cage damaging both lungs and she hobbled20-25 yards before falling. So no you don't need 150 grains to effectively harvest game in the 200 yard range. However what you do need is accuracy which may or may not come at the higher power loads, confidence and to know your abilities both ballistically and personally. So you'll need to shoot/practice at 200 and find your happy medium. Please remember the size of the projectile from a 50 cal Ml is highly suspect to wind drift so don't just shoot it at in perfect range conditions, be real so you know your limitations when it matters most in the field. Personally unless the situation is absolutely perfect I won't attempt a shot of this length...to me this is broadside/standing, minimal wind, solid rest and confident about the shot that ensues. If I ain't 100% sure of a positive outcome I don't slide the safety off, regardless if it is within my practiced abilities. IMO no sense chancing it and potentially wounding an animal.

Best of luck.