so how do they compare?
I had the classic 50s and an Avri 63 so ill actually answer this for you.
The pv 63 is the best pbass pickup i have owned. It has strong output of 12.5k and has a ton of low mids that have a ton of richness and depth. What this means is that with flatwounds like chromes you will get an ultra warm sound with crispness that cuts without needing boosted high end. A pickup with more high end that is nice but not as warm is the geezer butler. The pv63 pickup records so well that it basically mixes itself before even being touched by eq.
The output of the classic 50s is lower. It is a nice pickup. Gets that old school headhunters vibe, but it doesnt have the same detail in the mids. It is a very solid pickup but the pv63 is fenders best offering in years and is a perfect match if you are into the pbass w/ flats combo.