Hydraulic filter micron rating

[Cavalry]

I have a few pieces of outdoor hydraulic equipment. All is subjected to dirt/dust, condensation, extreme cold weather, etc. My filters are all over the place and I want to use one to keep inventory down.
I can go 33μ or 20μ with my local filter supplier. Most of the ones I have now seem to be 25μ. I would not mind going tighter(20μ) but I do not want the filter in bypass either when its getting dirty or 0* outside.