Now, I just played a blob list against GK's with purifiers, I had 2-20man conscript squads, shielding my 30-man commissar Power blobs, my enemy moved well and decided to assault 1-30 man and 1-20 man squad each with a squad of purifiers assaulting each. I also had straken in this list and his Counter attack went off on all 4 of my squads, and I was able to wipe both squads of purifiers while sustaining 25 casualties to one 30man blob(cuz they failed to wipe the 5man purifier in one turn) and the other purifier squad was wiped while losing about 10 casualties.
I then proceeded to recycle my conscripts and my blob squads killed off the other purifier squad, so for his 260ish pts, it cost me about 150ish points(plus recycled conscripts depending how you feel about them), so even though Cleansing flame went off twice on one 30man blob, and once on other 30man blob, my commissar blobs got stuck in/wiped him, while I was able to recycle my conscripts next turn(b/c he can't sweeping advance if the commissar blob gets stuck in) while also wiping some of his potent assault potential. So, I would say Power blobs are stilll the way to go, as they consistently can cause many invuln saves and also regular saves to elite units.