You know I was having the same problem trying to get the fine chipping down. What I was doing was sharpening the point of the pencil with my no.11 modeling blade and somehow, though it look pointed, it wasn't giving me the effect i wanted. So, in a personal moment where the common sense light bulb went off over my head, I grabbed my son's pencil sharpener one day and started grinding away. I didn't use the pencil sharpener before because I thought whoa that thing is going to reduce my $6 pencil (which are not always easy to find )to a runt of its former self but I said to hell with it I am going for it. The pencil sharpener didn't take that much off and it just gave me a sharper point and thus increased the likelihood of achieving a finer chipping effect.
Thus I guess my advise is use a pencil sharpener and frequently keep it sharp because as you know the lead is very soft and dulls very easily. Also, I found very slight hand movements worked best. For instance I place the pencil on the area I want to chip and move the pencil along slowly in a line then slightly move it at a right angle to the line of movement if i want to show a jagged chip.
So, Here are my final pictures of 5V-X. I added the bombs, canopy, windscreen, landing light lenses and other sticky out things and some further weathering as well as finishing off the canopy rails which I added with evergreen styrene.The whip antenna is made from stretched sprue (stretched to about 2 feet to get it as thin as I wanted) and I used Terry's (Airframes) technique for doing this which included dropping some white glue at the base of the antenna and painting it after it had dried. The light behind the cockpit head rest is missing in some shots but I added it later. You can barely make it out in the bottom pics.
Also, I want to thank everyone who contributed to this build with their references, tips, suggestions and general comments. They are much appreciated.
Thanks very much for all your kind comments. I got the stomach flu shortly after posting the above pics and with my wife out of town it was a week from hell. Having to pull double duty while being sicker than a dog was not fun. My daughter got sick with the same thing so it was really gross. I am feeling better though. Glad I took today as a vacation day at work. At any rate onward and upward.