30 more cannon rounds would get you 3 kills per ammo load and let you think about a 4th, instead of 2 and think about 3.
What about my 20 ENY P47? HMm? 
The D40 is a totally different plane. Its along with the D25 and the N, are some of the best bomb-trucking fighters in the game. And they have bullets to spare, so that you can take low percentage shots any time you feel like it. The Yak 9, either of them, cannot do either of those two things.
I've flown the Yak 9U as my primary ride the past 1.5 tours, and I plan on keeping it my main ride for the October tour. Its got great speed which is hard to appreciate until you fly it. I know when I looked up the Yak 9U on Soda's page a year ago and didn't see a red line on the speed/altitude chart, I discounted it immediately.
The guns package makes it even easier to discount it. Lets face it, one cannon and two 50cals (which they basically are), with very light ammo loads, is a poor, poor, gun package. Its comparable with the A6M2, which I flew extensively in preparation for Rangoon. The Yak 9U has the same number of cannon bullets, but all in one cannon instead of two, with the plus side of MUCH better ballistics and spinner mounted. It also has very little machine gun ammo, compared to the A6M2 which has tons of ammo of a small caliber. So its practically a wash between those two.
And anyone who has flown either will say the guns package makes it very difficult to rack up more than 3 kills. There just aren't enough bullets to pull it off. There's been SO many times I've blown my ammo load trying to get one airplane who's 500 off my twelve and I just can't quite hit them enough to kill them.
Also its hard to really saddle up on someone when A) most fighter planes that are slower have a better roll rate, and B) they can afford to take the Yak 9U's best snapshot as they give up a brief guns solution, and C) they know both of these two things. So they give you a quick shot, know they will likely survive, and scissors their way behind you... I'm still trying to figure out the counter to it. Since you must be sparse with your shooting, it also has the weakness of getting more assists than the pilot deserves, instead of kills.
The reason I fly the Yak 9U of late? My gunnery needed and needs improvement. They Yak 9U punishes bad gunnery, simple as that. If and when I land kills, I did something right or I got lucky proxies.
All this said, its a fun plane to fly due to the sheer speed that doesn't sacrifice all your manuverability. Its fun to try to outfly someone on your six by diving to the deck and flying through hangers, between trees, under bridges, knowing their plane is too big to follow you (or they have a smaller margin of error), all the while hoping you don't screw it up and crash. And being 20 base ENY, it racks up good perks (not that I spend any perks). I think its a great plane to fly given my progression to date as a virtual fighter pilot. Its just hard but fun.
