Here's a bit of information on judging distance.
The default gunsight will tell you when you are pretty close to 300 yds from the target aircraft. Once the target aircraft spans the width of the outer circle of the sight, he is pretty close to 300yds.
Keep in mind that it is not "precise," as a larger aircraft ( buffs, goons etc) will of course fill the sight before you are that close.
However, if you go off line and mess around with your gunsight, it can show you alot of information. You just have to be aware that it's there.
As far as the hit sprites showing through the cockpit, I kinda miss it too. But.....I like the fact that it is more realistic without them, and presents more of a challenge. It was a crutch...gonna try walking a bit without it
Cheers,
RTR