queeny

Going back to your original choice like you say probably a bit overkill for tuna but that's not saying it can't be used.  Any extra lifting power is sometimes handy when a half decent one starts circling under the boat (though the boat should be driven off to change the angle to one better suited).
 
That rod (PE5-6) is probably just a tad heavy for 50lb but still very workable (PE5 would be about spot on even thought it is slightly overrated for 50lb as for kingies I'd rather a bit extra than a bit less)
As far as kingies go generally you should be looking at a setup to handle either 50 or 80lb line. 
 
That being said consider drag should be set 1/3 of the line (albeit you may need to clamp a hand on the spool at times but this can be instantly released if needed).  1/3 of 50lb is around 16lb and 1/3 of 80lb is 26lb.
 
Get an 80lb set up and tie it to a set of scales hooked to the base of the clothes line and see what you can pull the scales to. - bet you'd be battling to pull anywhere near 26lb drag on the 80lb.
 
what does that mean - 50lb should be adequate in most situations (unless your in real rough territory) and a decent wind on leader will protect you at the fish end.

YFTV great tuna and snapper videos. Really take the time to explain stuff.

YFTV great tuna and snapper videos. Really take the time to explain stuff.

If you still have not broken the 40cm mark by the end of April PM me. If you don't mind a trip down to Goolwa I can pretty much guarantee you a few in one session. Ill take you young whippersnappers to my local monster bream spot

If you still have not broken the 40cm mark by the end of April PM me. If you don't mind a trip down to Goolwa I can pretty much guarantee you a few in one session. Ill take you young whippersnappers to my local monster bream spot

Not my footage but worth a watch

Not my footage but worth a watch

Not my footage but worth a watch

Not my footage but worth a watch