Upgrade From SME IV to V - Worth It

@dogberry I agree with @ pindac. There will be cartridges that actually work better in the IV, but the differences are minor. Both are very good arms. I think the Tri Planar, the Reed 2G and the Schroder CB would be significant steps up, but again that money might be spent to better effect elsewhere. 

My take on the IV is that it served a few purposes as follows:

1, I was in possession of a TA that was claimed to be competitive with the best from the era it was purchased.

2, There was a pride in having been the owner / user of the TA.

3, I was not shy to make it known I had a IV in use and did not sense the need for many years of ownership to investigate changes that could be made for it.

What changed I investigated upgrading the owned IV, from recollection there was discussions about ADEC 7 or even ADEC 9, as well as reproducing some critical parts from different materials, to be produced to extremely tight tolerances, using a very stable material and polishing this material to not usually produced surfaces finishing.

At the same time I was introduced to a TA, that had been created using a selection of the methods on the table for the IV, following the demo' of the TA compared to the IV, I was immediately convinced the IV was to be superseded, which it was.          

IMO upgrade the phono stage you get much better results

@mgattmch The Gyrodec is a fine turntable. You can not do better without spending insane amounts of money. I know your cartridge well. What I would do is keep the IV and replace the Maestro with a Soundsmith Voice.  The Voice is as good as many highly touted MC cartridges. It is high output so you will have an excellent signal to noise ratio and it's tracking ability is unsurpassed and it is much less expensive to re-tip. 

It depends initially on the period of origin of the IV, initially the V had Abec 5 bearings while the IV had Abec 3 then over time they made improvements to the entire V IV and 309 series.
I would keep the IV replacing only the original wiring with pure silver and investing the money saved in an upgrade of the head or phono.

the V has some more features as standard (silicone damping tank not necessary because if badly adjusted it suffocates the sound) possibility of VTA on the fly, lower tolerances than the IV but not to be heard obvious differences that do not let you sleep at night, VDH cable in silver; according to several enthusiasts who have had the V it seems to sound more  soft compared to the IV but these are nuances.
Changing the head for the better you notice more differences than going from the Sme IV to the V