Went through this same exercise. It eventually boiled down to the following:
- E-race w/centers. I only heard the axle back in person. Deep, throaty, more like an AMG. Loud, but not obnoxious.
- Akra Evo. Higher pitched, exotic. Turbo more pronounced through exhaust. Closer to the E60 (S85) "metallic" sound.
- Meisterschaft w/LXR center. Midway between the two above, throaty and exotic. Louder than the Akra with the valves open, not quite as loud as the E-race axle back.
I too definitely suggest listening to these in person if possible, under load. Stationary revving is not quite the same as when rolling.
Current: '16 GT4
'13 F10 M5, Alpine Weiss III/Sakhir Orange Full
'10 E60 M5, Space Gray/Black