At the risk of being rude, I think that with all those direct 88mm flak hits any B17 wearing this skin should be in pieces, not flying.
It's really easy to overdo damage effects. One or two big holes might be appropriate on a plane that size, but not as many as you've got. Remember, the B17 is a big plane and even a .50 caliber ball bullet is going "only" going to leave a hole the size of your thumb. A 20-30mm cannon shell will leave a bigger hole as it passes through, and perhaps a hole the size of a man's head if it explodes on contact. That means on the B17 skin, bullets are going to look like little pockmarks, while evidence of cannon shell explosions are going to be no bigger than your thumbnail.
Also, a bullet or cannon shell going through painted aluminum isn't going to leave that much carbon behind. Instead, you'll have an irregular area or circular area where the metal is deformed and the paint is blown away allowing the underlying metal to show. Don't be fooled by some of the ugly damage textures you see in IL2, which make the plane wearing them look like moldy swiss cheese. Instead, think of a bullet or shotgun blast going through a road sign, like this:
http://farm1.static.flickr.com/17/20517346_8c57099a26.jpgor this:
http://i.telegraph.co.uk/telegraph/multimedia/archive/01467/roadsign-shootings_1467286c.jpgWhat is good about your textures is the attempt to make the metal around the blast look deformed and you're making a brave attempt to how just how much damage a big bomber could take and still (sort of) fly. The problem is that the deformed metal effects and big black spots aren't going to look so good up close on the 3d model unless you can alter the 3d damage model or the alpha layer of the damage skin - which is much more involved than just making a skin for the plane.
Given the limitations of modeling damage using just a skin, it's another reason to go for subtlety. Instead of big black holes, consider creating effects which make it look like a shell entered the plane and exploded, sending shrapnel in all directions without making big holes in the skin. That would make it obvious that the plane is in deep trouble without making the skin look unrealistic. Obviously, you'll want to limit this sort of effect to non-vital areas of the plane, like the nose, rear fuselage, wing tips, tail or vertical stabilizer.
There are lots of good pictures of badly damaged B17s here:
http://www.daveswarbirds.com/b-17/fuselage.htmThat should be a starting place for your to get the effect that you're trying for.