While i dont have hands on experience with either, I spend most of my days looking up the different between the SVS lines, and PB vs SB within those lines or PB vs the SB of one line higher.
The end result is pretty consistent and universal to all svs products. The PB always has more to low end output than SB from the same line unless you have money to get multiple SBs, but SBs are cheaper at the higher lines. PB vs SB of higher line usually goes in favor of lower line PB. And line to line difference is consistently noticeable even with PRO model, except 3000 to 4000.
People argue that the PB 3000 measures better than 4000 in some areas according to what I read here and there. That said, some say the PB 4000 puts in less work to put the same amount of bass out, anecdotally and is the better product money aside.
SVS seems to make an upgrade to the next series enough of a vertical upgrade to make it worth it. They seem very careful with making sure that each product builds up to the next without overlapping.
All of this is anecdotal and unscientific. But people seem pleased to upgrade within the SVS brand at all levels. The 3000 is considered special among all the models. Perhaps it is the sweet spot between budget and performance. If I was strapped for cash id save up for this bad boy as the end game sub.
Personally, I whipped my credit card on the table and got the PB-16. My wife wants a second one, which of course I want as well. This subwoofer taught me a lot about value in audio equipment. Ive never regretted spending 2.5K on this sub, and neither has my wife. And to put that into perspective, our next most expensive purchase was the entry level klipsch towers for 300 several years ago. So it felt wrong to spend that much... until it showed up. We knew it was worth the price before we even unboxed that bad boy lol.
TLDR: go up in model numbers as far as you can afford; dont cut price corners by going SB even across lines unless you can afford several, if tactile bass is what youre after, though SBs are not considered weak sauce either. PROs seem to always be noticeable upgrades, albeit not as good as the next line up.