Regardless of cartridge choice, you’re going to need to replace everything else to hear what a planar 3 can do!
or not be too enthusiastic about replacing everything in case you get to the limits of the rega and then have to upgrade the rega.
I have done that several times – bought some external x-overs for my speakers, then had to upgrade all the sources and pre-amp as they were not now good enough and you could hear it.
And such an upgrade does not necessarily come with as much of an improvement in your listening experience as you might hope for – witness how many people used to enjoy their NAD 3020s which had a nack of making everything sound pretty decent, even though they were pretty modest performers.
Best to always have the source a bit more capable that the downstream system I reckon – as long as you are enjoying the music.