If you look here it is sis that particle size is largest 0.1micron
http://www.konicaminolta.com/inkjethead/technology/report/pdf/icis_200205_tomotake.pdf
This shows largest as 2.87microns, some 0.6 some
http://www.slideshare.net/HORIBA/particle-size-analysis-of-pigments-and-inks
This chart below shows particle size from 0.1 to 0.5microns
This however claims that particle size is mostly about 0.2microns
http://scholarworks.wmich.edu/cgi/viewcontent.cgi?article=1007&context=hilltopreview
So that means that 0.45micron syringe filter would make your ink very good if there are particles that would pass the filter, otherwise you will just clog you filter.
The idea is to filter mostly DYE ink because you never know if the bottles were clean, ink top quality, no residue after a while, no oxidation occurred, no impurities go into the ink etc.
Suggested filter process:
Take 50cc syringe and suck ink into it.
Attach syringe filter and inject ink into virgin cart, cis system etc.
wash the filter reversed with distilled water. Dry filter, reuse if possible.
It seems that 0.45micron filter diameter 25mm can filter 70ml of liquid with unknows particles (claimed by manufacturer) and cost is about 1-1.5$ for a filter, not that bad.