Ok ok ok. I concede to your wisdom and experience. Let’s change the topic a bit then and what cabs would you recommend to pair with the 400rb-iii? I’ve researched that on here too and mainly seen the GK neo stuff being recommended. What else should I look out for?
Welcome to TB! The place you go when you didn't know you wanted gear until you read about it!

You're gonna go far, being open to advice on here (not being sarcastic), so I won't beat the drum of what everyone else said, but I'll try and contribute on something I didn't quite see covered yet....
If you need silent practice, what
exactly are you after? Do you want to mix in other music (tracks from your band, your favorite songs, etc.) or JUST your bass signal? You're in good shape on this since you have a passive Jazz bass, a lot of solutions right out of the box. If you aren't looking for a specific or super tweakable tone, many small practice amps (Fender Rumble series 15w, Ampeg BA108, Ashdown Tour Bus 10) will have aux input along with a headphone output. TONS of pedals (like the Zoom pedals, which are quite affordable) have this feature, and there's the headphone amps from Vox as well. Most all of these solutions are under $100 new and can be had for even less on the used market. Trust me, there are TONS of those practice amps out in the wild, as they are the go-to for most people who start and quit playing two months later. This way you aren't breaking the bank and you can still keep the 400RB, might even come across a pedal that gives you both a great tone for your amp's front end AND silent practice options!
As far as the cabs question, I personally find the Avatar neo cabs to be my favorite for GK gear. To me, they sound more aggressive than the GK cabs, but that in no way says the GK Neos and CX series CANNOT get aggressive...they just tend to have a rounder low end and "sweeter" highs in my opinion. Several great cab companies out there, but a garbage set of speakers can ruin an otherwise fantastic setup. I will probably get some flaming from others, but I'd steer clear of the Fender Rumble cabs. For vintagey sounding stuff they are ok, but the
built-in midscoop of the cabinets themselves can be quite annoying, resulting in less cut for you when playing with a band. Some people claim the GK cabs have a midscoop, but I can tell you right now I thought my Traynor YBA200 was broken until I hooked it up to my Kasino 2x15s w/ Eminence Legend speakers (I am comparing this to two Fender Rumble 1x15 cabs).
However tons of great options are out there, Markbass can be pricey but quality, I hear good things about Aguilar, Eden also makes a good cabinet, but for your purposes I might suggest two GK CX115 cabinets. Pretty affordable, solid tone, and should get plenty loud. If you want to spend a bit more, 2 GK Neo 1x15s (or a pair of Neo 2x12s ideally) would be great. Some Avatar 2x10 neo or 2x12 neo cabs would be my choice, but some more of the "premium" cab companies like Markbass, Mesa, and the higher-end Ampeg cabinets would also do a good job. Ideally, take your 400RB to Guitar Center or Sam Ash, ask the staff if you can try it out on some different cabs, and take home whatever sounds best to you! The best judge is your ears, so use them when you can!
Welcome to the low-end! Best of luck on your cab journey!!