Why not both?
PBO is just a name for AMD overclocking:
FMAX will raise max clock (read: multiplier) by 200mhz (+2x). By default your clocks won't jump higher than 55.5x100 (x3d side) unless you do static or ECLK
And CO/Scalar regulates how aggressive your board undervolts CPU and willingness to give more voltage (and clocks)

With ECLK you swap 100 for 101 (or 102, or 103). It will obviously render previous CO offsets useless, but you can re-test it.

I'm running PBO+200 with negative CO and ECLK of 102.5. CO values are pretty small though, just to allign VIDS closer (there's single voltage rail, so all cores get same voltage).

 

Why not both?
PBO is just a name for AMD overclocking:
FMAX will raise max clock (read: multiplier) by 200mhz (+2x). By default your clocks won't jump higher than 55.5x100 (x3d side) unless you do static or ECLK
And CO/Scalar regulates how aggressive your board undervolts CPU and willingness to give more voltage (and clocks)

With ECLK you swap 100 for 101 (or 102, or 103). It will obviously render previous CO offsets useless, but you can re-test it.

I'm running PBO+200 with negative CO and ECLK of 102.5. CO values are pretty small though, just to allign VIDS closer (there's single voltage rail, so all cores get same voltage).

I have 1 Core that needs + CO to be stable with 102 eCLK so was just wondering if its worth it, or whether its better drop eCLK for it to go 0 CO or negative

 

Precision Boost is the name of AMD boost algorithm. Precision Boost Override through various parameters allows to override stock precision boost behaviour.

I use ECLK to get higher FMAX then what +200MHz allows.

Negative CO to gain better sustained boost, ie fool CPU SMU to think cores are better then they are.

Positive CS to add voltage to aid stability. Setting CS is the hard part.

Due to the BCLK change the CPU will not use negative CO values it can sustain at stock BCLK. But negative CO is still needed to sustain/ehance boost behaviour.

Due to the BCLK change, the whole CPU frequency range will get an uplift. So every CS frequency and temperature point/band will need positive value to add voltage to voltage frequency temperature curve, that adaptive voltage frequency scaling uses to stabilise precision boost.