My previous experience with flowmaster (not flowmaster 70 nor in a h2) is they are inexpensive and loud! Although i did not dyno it but it almost felt like it didn't have much backpressure so i was losing a lotta low end power.
I do have the Borla dual tip exhaust on my '03 H2. I do like the sound of it. It's a little louder and deeper at idle and driving around town. And when you mash it, it's still not obnoxiously loud, it is just right to me. The down side is they are not really "bolt on", it's more like "clamp on". So it took forever to align the two tips on each side. And now that they are align, the two pipes underneath are touching each other so there's a rattle sometimes
I am sure i just need a few more hours of crawling underneath the rig and do some more twisting and stuff...
Combined with the Edelbrock headers and a Trueflow air filter, the gain is definitely there and the powerband is just better all around. Especially compared to stock, it just felt constrained.
Oh, make sure you stay away from Borla headers, do a search cuz i just made a commment on it few days ago...