Disclaimer: I’m not a an engineer. This is all hearsay!
I used 3DXTech brand CF+PETG in my LR2 refresh and posted about it here. After 2 Years, LR2 Gets a Rebuild in Erie, PA
You’ll even notice a remix of your endstop blocks on it! (at least I think you designed them)
Here’s some data sheets. I couldn’t find a bog standard PLA data sheet. This PLA blend mitigates some brittleness.
The basic low down is that, on paper, CF+PETG is stronger and more rigid than PLA which is represented by the tensile modulus and flexural modulus respectively. Other benefits are a much higher heat tolerance and the superb layer adhesion you get with PETG. It’s also surprisingly easy to print and the CF acts like scaffolding making overhangs look great! And damn that matte finish looks cool…
If heat tolerance doesn’t matter to you, how about CF+PLA? Not as strong as PETG but more rigid than both.
If any of that matters for the LR3 I don’t know. But you wouldn’t be making a mistake by using CF+PETG on your build. Just make sure you get the quality stuff like 3DXTech. Cheap stuff might just have pulverized CF for a matte finish.