By your own admission the delta v between the .30-30 and x39 is inconsequential.
The same delta v exists at 150 grains. The velocity diff isn't much and isn't of any consequence.
With 170s, I don't know as I haven't loaded that heavy in the x39. I do shoot them in my .30-30 because I don't like the performance of the only 150s I've tried (Winchester Silvertip of 1980s vintage). The 170s stay together better for me, but they still act about the same as the 123s have for me in the x39. You don't need 170s in the x39 because the velocity is low enough with the 150s to be very easy on cup and core bullets.
In my experience the 150 fps bonus gives very little advantage as far as penetration goes, and if anything, the extra velocity usually results in greater expansion which is counter productive to penetration. It's all hairs we are splitting here.
I can't argue this anymore. It's pointless.
I hope you have a great thanksgiving.
