I've shot Delta 4 blade for years ........... they are a great head ........ not hard to sharpen , hold an edge well , fly true , no penetration issues ........ what more could you ask for ?
I have always prefered 4 blade over 2 ........ I know the theory is the 2 blades penetrate farther BUT if any head produces an exit wound it penetrated far enough ........ and a 4 blade has the extra 2 blades cutting a larger area than a 2 ........... I always picture in my mind a 2 blade passing just by an artery but parralel to it ! .......... to me the extra 2 blades add a little insurance
With deer sized animals extreme penetration is not required . If I was gonna shoot a moose with lighter poundage I might consider a 2 blade .
Bottom line is the 4 blade Delta is a fine head , the extra 2 blades are relatively small , and you still get great penetration !