i own both Avenger and Avenge-x . go with the Avenge-x for all the reasons discussed above and the good discussion/disclosure on Pyramid site. BTW, both my guns are super acurate out to 60 yards with 18 grain JSB and AEA (i recommend AEA)
I have the same questions...I know the 550mm barrel shoots pellets well, but how about the 700mm barrel (i like that the longer barrel has larger plenum but if it is really designed for slugs i will get the 550 mm barrel)