Buy both and try them out! You won't be disappointed with either, they're definitely not chems that'll get chucked in the back of the shed and never used. SPM is your everyday stuff, shockwave for the real mingers. I used shockwave on an Indian restaurant carpet that I've cleaned about 12 times previously... it out-performed powerburst.
I would still keep powerburst as a fall-back, just for peace of mind if nothing else.