Ok, I have a  norinco MAK 90 (7.62)  and a waffen werks 5.45  Like them both a lot.  a few observations:

At close range lets say under 100 yards, 7.62 probably has superior terminal ballistics.  it's a big, relatively slow bullet.  I can shoot bowling pins with iron peep sights at 100 yards with it and generally drop 10 with 1 or 2 misses.  As i recall, it's about a 2 moa gun with wolf or tula. never shot anything else through it.  You are asking a lot of it to engage targets at 300 meters, however.

5.45 "flight path" is much flatter, similar to 5.56, but the bullet is longer.  5.45 has a greater effective range and is more accurate at longer ranges.  ammo is lighter, and i would speculate that somewhere a little beyond 100 yards, the 5.45 would do more damage, especially if you are shooting 7N6, which is a bullet that is designed to jack knife.  This round really proved it's worth in the russian afghan war and the afghanis called it the "poison bullet"  So it's a battle proven capable round that in my view is considerably better than 5.56 at making a big hole.

so, If my golf bag of guns is sitting right there while the screaming hordes are running at me, Under 100 I'm reaching for 7.62 with a hollow point, preferably.  If they are further out, definitely 5.45

those gel blocks were probably shot at very close range, and 7.62 makes a huge hole up close like that, but 7.62 x 39 starts to run out of steam pretty quickly compared to 5.45.

And, as a final thought, the russians don't use 7.62 anymore, and the track record for 5,45 is pretty impressive (with 7N6 ammo)

7.62 is available everywhere however, and is usually at least a a dollar a box cheaper.  and, most gunfights happen at 100 yards or less.  My bowling pins fear my mac at that range...

Agree with the sentiment listed above.  also, I do not find 5.45 to be more accurate than 7.62.  I have guns of both calibers that shoot 2 m.o.a. or in some cases a little less.  My 2 most accurate AKs are both in 7.62, but one is a mak90 and the other is a VEPR, so I would guess this has more to do with heavier receiver, trunnion and barrel than anything else.

I do think 7n6 is a great round that makes a wound channel much larger than it's caliber would suggest, and is better at extended ranges than 7.62 because it shoots flatter.  It seemed to work very well during the russian afghan war, and certainly better than 5.56 military ball.

I also find it interesting that 300 black out is so popular and people love to talk about it's stopping power, etc.  then these same will deride 7.62 x 39.  

final thoughts.  I shoot a 5.45 AK in 3 gun, and since the 7N6 ban, ammo cost is about on par with 5.56.  a 20 round box of red army standard at cabellas is nearly 7 dollars, while RAS 7.62 20 rounds is more like 4.50 at cabellas.  

5.45 is much harder to find offline than 7.62x39, and it tends to be significantly more expensive.  I'm considering switching over to 7.62 for 3 gun for these reasons.

Still like my 5.45 and It is sweet shooting for sure, and easier to shoot fast than 7.62 due to minimal recoil.  If i could only own one?  probably be my mak 90 in 7.62

I have over 7K rds of this 5.45 ammo that I bought back in the day assuming I would get the rifles for that caliber (AK74). Never did get those in that caliber. So now I am trying to get rid of all that ammo I have no use for LOL
Posted in couple of sites that its for sale. Maybe someone wants it. I rather exchange it for 5.56 and 7.62 mix. Since I have 3 weapons in 5.56 and one AK47. I have been coming to this site for a long time but I am not active in the forums or whatnot. Now that I just dug out the ammo that was buried in the back, decided to get rid of it. Let me know.