I can't imagine it'll take much off, push and pull and radiators usually drops another couple of degrees from my testing. I would think that you would get about 2- 3 degrees cooler going push pull vs just one.
In
optimum Tech's video, he got about 5° less by adding a nf-a12x15 on top of the nf-a9x14 (bottom). This config is pretty much on par with a noctua l12s I believe you'd be better of with dual nf-a12x15. From
Guck's TV's video he got about 5° difference from switching the bottom fan to a nf-a12x15 (no top fan mounted) so if you go with dual nf-a12x15's I think 2-3,
maybe 5° , if your lucky, would be about the best your going to see.
At this point you will be only a couple degrees cooler than the l12s, and wether or not the massive increase in cost.... since it's ~$35-40 for 2 fans and either lower speed (compared to a decent 3200 cl14 or even 3600 cl17) ram or super expensive vlp ram (with more potential for overclocking) when compared to the bent/modded l12s.
Or even a bent l12s + vlp + nf-a12x25