Cartridge for RB300 other things


i just purchased a used planar 3 w/rb300 arm(no mods) and would like some opinions about a suitable mm
cartridge (300-500 $'s). i currrently have an ortophon om30 and it's ok (a bit bright). also i'd like to replace the felt mat with either a ring-mat or audioquest sorbogel mat-what are the merits if any with either one of these and how can i adjust the vta for the mat & or cartridge. also if some one could pass along any other tweaks
that would improve this tt-thanks
vellum
I have the same setup and just purchased a Dynavector 10x4mkII. This is a great match. I also own the Benz Glider and feel the Dynavector is a better match for the Planar. Have not experimented with mats but I do know that the importer for Rega (lauerman imports) sells a VTA adjuster that fits on the bottom of the arm. So does VPI. If you go with the Dynavector which can be had from the Needle Doctor for $280 with trade you need one spacer under the arm and I have a feeling after hearing this cartridge you will not be taking it off the table anytime soon and dont need the VTA adjuster.
I think the above suggestion is a good one. My dealer recommended the Rega cartridges, and I know others use the Sumiko Blue Point special.
Rega recommends several different cartridges, including Dynavector, Grado, and Sumiko. I have a RB900 arm, and use Grado and Shure V15VxMR cartridges which both work well.