5th Brother vs Average PT era Jedi master

I still have to understand where the general consensus here puts the fifth bro. I mean, i saw people say the he could only take on Jedi knights and padawans, while GI and Vader dealt with Jedi master tier Jedi or above. Others put him higher, capable of defeating the likes of Secura etc. So, what do You think? Can he beat a master? If so, Who is the strongest guy he could beat?

5th Brother should be average to strong Jedi Knight level. He should be capable to deal with most Knights and perhaps some non combat oriented masters.

GI should be capable to deal with most masters.

Aren't they supposed to call Vader if they encounter a master?...