I think my little piano demo is a little hard to hear the differences because of the background noise of my apartment. What I have found over using my modified deck over the long term is that while the self-noise didn't really change audibly, the quality of the treble range improved significantly as did clarity overall. I'm not sure how much if at all you'd hear this with an amplified rock show, but I hear it in all of the choral recordings I do. When my 70D was stock, I would absolutely prefer my FP24 > M10 chain. Now, straight into the modded 70D wins.
I hate to use a silly audiophile trope, but the difference in my recordings before and after the mod remind me a bit of the "veil being lifted."
In all seriousness, it's sort of like with and without heavy wind screens on the mics.
The specs on the opamps used in the 701D are close to those used in the JW mod. Whether those opamp specs or the added caps amount to anything was the subject of much discussion in the mod thread linked above if you're curious.
Bottom line for me, I'm happy to have gotten the mod and the improvement makes it the best recording chain I own for the music I record. As always, YMMV.