suicide_boy...What are you riding?
How me and the local dealer got talking about brakes was I asked about putting dual discs up-front on a Heritage Softail. This is what I learned from the conversation. Stock calipers have two piston, PM's make a four caliper. By upgrading to a 4 piston caliper you will essentially have dual stock calipers. It would be a lot cheaper to upgrade to 4 piston calipers then add dual discs. Something to consider before you add a second front disc brake setup. Right now I am thinking I am going to go with the 4 piston caliper for two reasons. One, it's cheaper than adding a second disc brake setup. And two, there won't be a second disc to hide my wheel.
I agree with you about adding more stopping power, especially if you add more HP to the bike.