How do you decide which acoustic material to use?

I'm currently in the process of getting some quotes for some Fibrex 1200 series panels - 1240 and 1280. I'm assuming the 1240 is the 4#/cf and the 1280 is the 8#/cf the guy at SPI Dallas references. Here's the properties of each: http://www.fibrexinsulations.com/technical/acoustical.html At 4 inches of thickness and between 250 and 1000Hz, the 1240 has better coefficients, however at 125Hz, the 1280 is much better (as expected). Above 1000Hz they are almost the same with 1280 leading slightly, but not significant enough to be noteworthy. My question: Since I have a small home studio (12.833 ft x 13.5 ft x9 ft high) to be used for mixing/mastering, should I opt to go with the 1280 on all my panels since bass will probably be the biggest issue - even the panels I'm using on my first reflection points? Everything will be 4 inches thick which will allow for trapping bass. The main bass traps, of course, will probably be 1280. Should I make this decision based exclusively on mode calc? I know either way I go, it will make the room sound much better, but what would you do in my case? Thanks in advance, Adam

I would use the cheaper of the two materials for everything. The differences are so minor. Frugally, Andre

Thanks, Andre!