Getting 4 - 6 kills on a single trip should be no problem with a Yak (forget about bombers though, unless u are flying the 9T). One thing I have noticed is that many people use the "spray and pray" gunnery technique... probably being used to fly the american rides with a zillion .50 cal rounds, or Nikis with 500 cannon rounds... times two. I could go on. With the Yak, you get an awesome cannon (either the 20mm or 37mm very fast and accurate, makes the german 20mm and 30mm seem inefectual) so all you have to do is get real close (icon range of 200 as a minimum... remember, icon range of 200 can mean plane is anywhere between 399 and 201yds), which shouldnt be a problem, and fire a short burst right into it. Most times, they will go boom, or lose parts they really need.
As far as shaking people off your six, the Yak is really hard to hit. I really hate fighting a Yak for that, especially when I am in a Yak myself since I have to be very careful with my ammo. You get a stick stirrer, and unless u can spray and pray, you are in for a long chase. But what if you are being chased? Get comfortable with the Yak's capabilities and figure out the relative energy of the fighter chasing you. In some cases, a simple barrel roll at the right time might do the trick. If you have a spitfire on your arse at guns range, with very similar E states, unless he sucks, you are done for. Same for some of the 109s. Best thing you can do if the enemy is in guns range on your six is remember that the throttle is another form of aircraft control and in some cases it doesnt pay to have it firewalled all the time.... and think 3D... flat turns are not the only form of evasive.
Anyway, as a general rule, keep it fast and use the climb advantage it has. 51s should be no problem... you should always be able to outturn them or outmaneuver them.
Emu
