Extended forktubes on a panhead frame

Getting ready to set up my frontend and I'd like to put longer than stock tubes on it. My question is how far of an extension can I do before I run into major handling issues? Not looking to go Captain America long with the motor tilted back, but a bit of extension would be nice.

For reference the frame I'm using is 0 up 0 out 30 degrees of rake. I'm reasonably sure it's stock panhead dimensions.

4" is not unreasonable. That's what these are.

No, that's not too bad at all, looks good. I wonder how it would be on a rigid frame, probably sit just a bit higher, I'd think.