There is a fundamental difference between a 200gr SW and a 200gr Powerbelt. The SW is only 40cal, so you still have a relatively long bullet...it's actually very aerodynamic for a ML bullet. The Powerbelt, on the other hand, is constrained by the need to remain full-caliber. So you end up basically whacking the back third off the bullet, leaving you with a short, stubby one. Not very aerodymamic.
When you cut from a 250gr to 200gr SW, you (in my experience) get a better ballistic coefficient AND higher velocity, so it's a win-win. With the Powerbelt, you get higher velocity but the shorter bullet has a WORSE ballistic coefficient...in other words, I'm (guessing) it doesn't shoot any/much flatter and hits softer when it gets there because it's slowing down a lot faster and has less mass.
To sum it up, I see no advantage to using a full-caliber bullet that only weighs 200gr. I'd either stick with the heavier ones or go to a saboted round.
For what little is is worth, my third-hand knowledge of light Powerbelts is that they have a reputation for blowing up. I've never shot them personally but hear sour first-hand accounts from multiple sources. In light of that and the rationale outlined above, I've never felt the need to try them (they're expensive too).
