Which Baitrunner are you using wheresmy50? The A series has a hard plastic barrel knob where as the B series has a rubber paddle for handle. It should say it on the spool of the reel. Spools between the A & B are not interchangeable.
I've used 30 lb Whiplash on my A series - worked fine but it wore a groove on the line roller. My B series has 30 lb Fireline (like rope) on one spool and the other is 17 lb mono.
Which braids have you tried on your BR 4500? Is yours an A or a B series?