Some of your assumptions have me puzzled. You ask for an intermediate powered cartridge, but suggest that the 7.62x39 might not have enough range. From my experience with that cartridge, I can assure you; if you need more range than that cartridge can provide, you don't need an intermediate powered round.
The 7.62x39 certainly isn't a barn burner, but I think it gets a bad rap in the range department. I zero my AKs and my SKS at 200 yards, and have no problem getting conistent hits with iron sights on five gallon buckets at 300 yards. At that range, the cartridge has the mass, velocity, energy, and momentum of most popular .357 Magnum self defense loads at the muzzle. If you need more than that, you need a full power battle rifle round.
And lets face it, 300 yards is going to be a long shot for you. The average engagement range in Iraq is only 60 meters, last I heard, and that's if you're a front line combat soldier. The average engagement range for a law enforcement marksmen is something like 75 meters. Again, thats if you're in a uniform. More than likely you're a civilian, in which case, you're going to have a hard time finding a situation where you will be called to engage, legally, beyond 25 meters.
And what you get with the 7.62x39 is greater effectiveness at these ranges. With a standard bullet weight twice that of the poodle shooters, you have more to work with. Depending on what you're going for, you can be much better equipped to blast through vehicle bodies and windscreens, cinder blocks and light masonry, and wood or foliage. The standard FMJ round for the stubby Russian round can pass through a typical unfilled cinder block or a foot of pine and still be lethal. On the other end of the spectrum, the right JHP or one of the newer rounds on the market, like the Hornady SST round, delivers terminal performance and fight stopping ability the 5.56 can't touch.
When you consider effectiveness, cost and availability, and range, I think the 7.62x39 is the best intermediate powered assault rifle round existent. There are some that have better exterior ballistics and even better effectiveness, such as the Grendel or the SPC, but they haven't attained the availability or economy of the Soviet round.
What it really comes down to is the platform you prefer. If you like the AR, then the poodle shooter or one of the less common higher caliber/performance rounds like the aforementioned Grendel, SPC, or the Blackout/Whisper, which in its supersonic loads is a virtual ballistic twin to the older Soviet round. I like the AK, and in an era when a lot of people seemingly strive to make their rifles more like SMGs, I still like my rifles to be able to do "real rifle" things, like shoot through stuff or reach and touch, so I go with the 7.62x39 for all the up-close and personal stuff (alongside a pair of Glocks and a Mossberg 590) and a an M1A in 7.62x51 for the reach and touch stuff.