I've never used a 30-30 on deer I just am not fond of lever guns. I have shot my fair share of 7.62x39 though. I use a 16" barrel AR-15 that I absolutely love. It shoots .308 diameter bullets very well and the best shooting bullet I've tried is the 135 FTX with CFE BLK powder. 2280fps and very accurate and 2 deer I killed with that load were shot at 25 yards and dropped quickly. Using a 123 .310 Gold Dot and CFE BLK you can get over 2500fps That makes it a 150 yard cartridge quite easily. I've always been told a 30-30 is a 150 yard cartridge. So I guess it's a wash.
I don't see much difference between them at 150 yard s or less, if you have a 30-30 you like then you will gain nothing going to a x39. If you have a x39 you'll not gain much switching to a 30-30.
So I take it you don’t see much difference between a 308 and a 300 Win Mag, or a 7mm-08 and a 7mm Rem Mag?
Using the OP’s criteria of 150 grain bullets, the 7.62x39, assuming a MPBR of +/- 3", you are talking almost 175 yards, the 30-30 will increase that by almost 75 yards. Using my load data here, but loading manuals and external ballistics charts will confirm it.
I recently loaded up a bunch of 147 grain pulls in 300 BLK, 7.52x39 and 30-30. All were zeroed at 200 yards. The rifles were a H&R AAC Handi Rifle, Ruger American Ranch, and the H&R Handi Rifle respectively. This is what the trajectories looked like.
300 BLK
100 yards +4.5" / 300 yards -17"
7.62x39
100 yards + 3.75 / 300 yards -14"
30-30 Win
100 yards +2.5" / 300 yards -10.5"
Again, ballistics tell the tale.
Note that these were .308 bullets. The only difference was the starting velocity. Had I been using .311 bullets in the 7.62x39 the trajectory would of looked more like the 300 blackout trajectory. The fatter bullet is simply shorter and has a poorer BC. FWIW, while true that some 7.62x39 Rifles shoot .308 bullets well, mine just does not. The 300 yard groups were over 7". The Ruger is the most consistently accurate of the three when using bullets it liked.