Okay, I'm still trying to get a handle on flying high-speed aircraft in the MA. Here's what I'm having trouble with:
I understand that the basic strategy is to come in with alt, dive down on a target, take a quick shot, then extend away, reverse, and repeat.
This part you have correct
1. My targets always turn away making a shot impossible.
The "trick" to learn is reading the enemy icons. Assuming there are multiple enemy below you and you are closing into the "furball" area, start looking at the icons. Pay attention to the numbers indicating your distance. Attempt to close to an enemy where the distance is decreasing. Use zoom for short periods to determine the angle of the plane.
Many will turn early, some will wait and break at the last second, others will pull up or spit S.
In the beggining..where you are now it will be difficult to construct a shooting angle that allows you to close into the turn where you get close enough to make a passing angle shot. Sometimes it will be very close, other times you will only get a d600 or so shot before the shot window is closed.
The best way is to get your nose down EARLY then pull up into the crossing shot. NOT late where you have to roll inverted or take a blind shot under the nose.
When there are slower friendly around break turning lower than you the enemy will always go for them. This is the perfect set up. If you pay close attention to the range of the enemy icons you can often close into the enemy without being detected.
Often you will make a pass on as many as 5 or more and all of them will be turning into you...just keep trucking...extend and come around for another pass. You may have to make 3, 4 , 5 or more before you get a good shot....PATIENCE is the key.
2. I'm having trouble reversing quickly in the FW A8 that I'm flying.
You should not try to "reverse" on them....ONLY create a closing crossing shot. The best way is to keep your plane fast...300 to 350...after the pass nose up to 2k of climb and extend. If you go verticle on a missed shot you WILL get caught by another enemy.
Sometimes you can get more than one shot depending on the enemy speed and where they are heading. DO NOT turn back into the furball to chase. Always keep your diving attack at an off angle form the enemy pack. If you do go through the middle make sure you plan the exit coming out AWAY from the base/enemy pack.
Could somebody also explain the difference between bnz and slashing tactics? I'm having trouble understanding it. 
I am speaking here in terms of OFFENSIVE gun passes. BnZ is more of a 1 on 2 type of combat. Slashing is just 400 mph strait throug taking targets of oppurtunity and extending off.
The correct way is to LEARN TO READ THE FURBALL....looking for icons that match a profile that allow you to close before they can make an evasive move...many will get check 6 and see you coming...but even these can be targets if you have the right angle and closing speed.
And remember.....nose low way early...easy pull up early and take a zero G shot...this is the key...ZERO G shot.