Re: Seymour Duncan p/u booster
It depends on your amp. Increasing your level before the amps input jack (using a pedal) will often add more distortion whether it is a clean boost like the SD Pickup Booster or any other OD pedal. When you add a hotter pickup to a guitar you add more signal and that causes the amp to work harder. The distortion isn't in the pickup, it's the amp working harder. The same holds true for a clean boost.
Now especially with tube amps but also with SS and hybrids you can only get so loud before the amp completely saturates and reaches peak volume. If you are operating your amp at its top end, this would explain why your OD is causing more distortion but not more volume.
Chances are, you're already too darn loud. Most players keep a reasonable stage level and then let the PA do the heavy lifting. This will allow you to use a boost pedal to slip over the top for solos.
If you are in a bedroom or in a band with minimal PA and your running your amps full out you may not be able to get the solo boost thing to happen and you are also working on distroying your ears in the process.
If you can work the level thing out, the SD Pickup Booster is a great way to go to get the extra level needed for solos. Personally, I prefer a good sound man at the board over a change in my stage level at the amp but sometimes a little extra gain from a pedal can be a good thing.