I've used 3x 2700X.
i) 1805 SUS (ie week 05 2018)
ii) 1825 SUS (ie week 25 2018)
iii) 1835 PGS (ie week 35 2018)
C7H WiFi with ThermalRight Archon IB-E X2 (lapped base), but 2x TY-143 and also EK Supremacy EVO block with 360mm slim rad, ddc pump, open air case.
1805 SUS was poorer on PBO Enabled than 1825 SUS, IIRC ~75MHz ACB gap, 1835 PGS sat somewhere in between. So I'd some difference but not vastly big. RAM IMC difference was greater than CPU MHz at stock or PBO enabled.
PBO: Enabled yields usually ~1830 - 1900 in CB15, 1830 say UEFI defaults (ie 2133MHz loose timings), 1900 is more like 3200MHz and even upto 3600MHz C15 1T I see no affect of increased RAM MHz on CB score.
1900+ is with BCLK tweak, 1947 shared for BCLK 103 seems on the money to me, as I have results like that. Below results will show RAM ratio in RTC 3466MHz as I used that ratio with BCLK 103 = 3570MHz.
Perhaps the >1950 CB15 scores you have are down to limiting VCORE, which in turn would allow higher boosting as create headroom within limiter parameters of PB/XFR2 stipulated by PBO being enabled. Will have to try this out.