I'm not sure that you fully understand the adjustable cam gear vs. the performance camshaft that both MVP and IPD offer. I also don't think that I'm the one to explain it, but I'll try. Of the two, you'd be better off with the performance camshaft. The performance cam will give you more power, but the adjustable cam gear as IPD says "allows easy horsepower and torque curve adjustment." You'd be able to dial in where you wanted the most power, either on the low end or on the high end. See these sites for some info on camshafts:

http://www.turbobricks.org/camshafts.html

According to http://www.volvonet.org/tpc/cam_data.html:

"The VX cam adds about 12 horsepower to a normally aspirated B23 or B230's output with no other modifications. When installed in a turbocharged engine, it probably adds at least twice that, especially if the car has benefitted from other mods, such as an improved-flow exhaust system or more efficient turbocharger."

If you haven't already done so, a good free flow exhaust will help (2.5" to 3" max). As for which company to buy from, find out which one will ship the cheapest, and see if they have any kind of sale going on because both offer the same camshaft.

Good luck.