Well 26sonic, I was asking myself the same question about 8 months ago. What I have concluded is that if money is not a problem, get both. I am in the process of getting a whipple, hydraulic steering and an XZ drive for about 10,12,,14; Well I don't want to know what the total is. In my conversations with Dustin Whipple he has stated that I would only gain probably 15 hp with powerflows. That is only about 1 mph for around $1600. You could probably gain 30 or 40 with headers and ECU reprogram, but they cost even more. So for me that wasn't enough. I wanted 10-15 mph increase not 2-4. It seems that the exhaust is more important with larger motors and naturally aspirated motors. It's all about speed cost money, but I think dollar for dollar, a super charger/ blower will give you the best bang for the bucks. However, you have to be prepared for the extra HP and speed. Steering for you and your families life, and drive (hopefully strong enough) for less maintenance problems. It is a vicious cycle and there is no free lunch. Oh yea I forgot about the Lab prop, man this is getting expensive fast.
So, I didn't answer your question. I would save the money for the Pro-charger and get the exhaust later. My .02 ,just be safe!