Of all the MM cartridges I have, I love the SHURE V-15 VMR the best. Before becoming mostly a MC man, I got a JICO SAS stylus for it. Not sure if you can still get them, but the last time I looked they had become stupid expensive. I think JICO has some other MR upgrades available. The SAS was definitely an eye opener and I stuck with that as my number one for many years.I never heard the V-15 IV, but read that it was a little bit of a step down from the III, so I think your going to love the V-15 VMR.
Disclaimer: the first good cartridge I evet had was a V-15 III MANY years ago, so my ears may have been preconditioned.
All the best, Jim