Dunno, my custom dual axial (cheap Armor variant from MSI) 2070 runs mostly passive, fans turn on at 60C+ and don't really go above 1500rpm under max loads with around 65C. Overclocked, 200W max.
Undervolting on AMD... you will lose performance, you can't magically run higher clocks at lower volts unless you were severely thermal limited which with blowers is to be expected. There is no fan profile adjustment on GPUs much, if you want custom curve it's all software adjustment of the fan, polling the GPU for temps. and sending updated desired fan speed to the GPU each second etc. That software, afterburner, etc. goes down and you get stuck on some last set fan speed, not good is it. Say you're encoding videos with post processing for hours, go away, come back thing is crashed fan stopped or barely spinning and GPU cooked itself... not a good day. Where as with fan being controlled by the VBIOS, by hardware itself, the fan 99% will keep spinning and adjusting even when there are software issues and crashes from instability.
Blowers are not worth it, ever. Any older cooler even from a 290 that people used on Navi (with no shroud) already is way better.
You won't get near 30dB with a blower and good cooling. Navi is in the high 40s while Vega was even high 50s dB.