Think of it this way: the type of mount your regulator uses serves essentially one purpose. That is to create an airtight physical connection to the tank. "Pro" valves, like the convertible yoke/DIN you've been using, are "200 bar," but clearly work on HP steel tanks.
Understand that the DIN conversion is simply a change to the mounting "adapter" on the reg - meaning the actual "regulator" portion of the regulator is entirely capable of handling 300 bar out of the box. It's simply that a yoke clamp isn't compatible with a 300 bar valve, because there's no commercially available adapter insert like you've got on your "200 bar" pro valves.
As to converting the regulator to "300 bar," all that really means is that the DIN adapter you install is the longer style DIN adapter. There
are 200 bar DIN regulators out there; I'm under the impression they're basically nonexistent in the US, and then mostly just ones that were hand-carried over by some of our European friends. A 300 bar regulator will work fine in a 200 bar valve. The only notable difference is that a 300 bar regulator's adapter will have 7 threads, where a 200 bar's regulator will only have 5. This means your 300 bar regulator will have a couple of threads sticking out of your 200 bar valve when it's tightened down, which is absolutely normal, and not anything to worry about.
The decision of yoke vs DIN isn't really one of "better" or "worse," in my opinion. It's mostly a preference thing. Some folks feel like yoke mounts are prone to dislodging from the tank valve if you bang them on something. I think that's an absolutely valid reason to choose DIN if you're diving overhead environments like caves or wrecks. Open water, is it really a problem? I'm not saying it's not, but if it is, I'd bet the problem is statistically insignificant when compared to other potential failures, including failures of the diver.
If you do choose to convert to DIN, and you ever dive tanks you don't own (i.e. travel and/or rent) you'll probably want a
DIN to yoke adapter, just in case you run into a tank that doesn't have a convertible valve.
I personally use DIN, and don't feel there are any appreciable drawbacks to that decision. If you have yoke regs and you show up somewhere that only has DIN valves on their tanks, you're hosed. If you have DIN regs and an adapter, you're prepared for pretty much every situation you'll likely find.
Edit to add: Also note that "300 bar" isn't something you're likely to find in SCUBA tanks, being 4,400psi. Some places/people throw around "232 bar" to encompass HP steel tanks, but that's even a bit off, at 3,410psi. I'm certain I've read somebody's post around here that explains the marketing (not logic) behind the 300, 200, 232, etc. Functionally, these numbers are nearly irrelevant on modern equipment, as pretty much every regulator has been designed to work with HP steel tanks for a while. Some more vintage regs might struggle with high pressures, but I don't think I've ever heard of a catastrophic exploding regulator caused by an HP tank.
