Cleon
Legend
It's not that far off from other elementals, though. We could tweak just a bit, if you like, but I don't think they should be several AC points higher than the highest SRD elementals. I suppose I'd be willing to add +1 to deflection at the smaller sizes and +2 or +3 max to the larger sizes.
I think the higher-grade Vacuum Quasis ought to be at least the same AC as an Air Elemental. I'm not so bothered about the lower-grade ones since their invisibility is more likely to make a difference.