Also, what is the terrain like where you intend to fish? The reason I ask is that I catch quite a few kingfish when slow jigging for snapper with very light gear (2500 reel, 10lb braid etc). I didn't write this to brag about my fishing playing skills, rather that I usually fish over sand, so there is no drama. The fight is long, but I get there in the end. I'm not suggesting you target kingfish with ultralight gear, but if you're fishing in "clean" areas, you can use lighter tackle which is more enjoyable, especially if lure fishing. 

That said, if you want to fish 7kg of drag routinely, get a reel that's rated for at least 10kg or so. This allows for two things: manufacturers, erm, exaggerate the drag capability quite often, and that many reels at their max drag are at their mechanical limits, and it's not healthy for them to be fished day in, day out at those levels.

one or two points on top of the excellent advice you've received. It's important to note that:

1. a braid that's labelled as 50lb will typically break at well above that - maybe at 80lb of true force. So don't try to equate the braid 'breaking strain' with force being applied.

2. If you set a reel to 20kg of drag (and there aren't many with that capability) and connected with a monster you'd probably get pulled overboard! A guy in the shop where i bought my old school TLD overhead reel for livebait fishing set the strike drag to 9kg, and that's a lot more than you think when something is pulling on the end. He had just spooled some strong mono (Momoi) on the reel and (admittedly I'm no Arnold S) but at 9kg I was falling forward off balance well before any line came off the reel.

3. Rozboon above made the great point that cranking a reel with "max drag" of 7kg specification to full drag would probably over-stress other parts of the reel (Japan-sourced reels usually say "max drag" and a significantly lower "practical drag" on the box, the latter for a good reason).

Great advice. 20 kg's would see me over the sio\de in a flash

Equally, it would probably give us a really good look at the cross section of our rod, just above the foregrip most likely

And as has been pointed out, worrying about the pound breaking strain gets confusing because of the manufacturers' claims versus the reality under mechanical tests. 

As others have said, go with the "PE" line rating recommended for medium to heavy kingie fishing and match that with the rod. The experts above recommend PE5 at least, which roughly equates to 50lb, depending on the manufacturer. 

Again, that's not because you are going to hoist a 49lb fish on the end of the rod into the boat - it's because of a whole range of factors. Others such as Rozboon and Mason have done the hard yards with kingies, so it's worth listening to them and not over-analysing.

Once you have PE 5-6 set in stone, you'll then have clarity over the rod and the reel for your set up. 

Once you have PE 5-6 set in stone, you'll then have clarity over the rod and the reel for your set up. 

 I personally use Jigging master rods and reels (PE3 and PE5 models) and PE5-PE8 braid with 80-100lb fluro leader ( no less for jigging), my own rigs on heavy assist cord, I've still been smoked by  good fish. But I've also been able to stop a fair few that had the heat on me, and I'm not a large human at 63kg.  Max drag setting I can deal with are about 12kg off the reel and that feels like its touch and go weather I'm going for a swim sometimes!  The JM reels supposedly can dish out 30kg or so but in the real world thats never going to be something you'd use. I usually set it so that I can just pull the leader off the reel by hand. a Nice smooth 8-9kg of drag will be all you need most of the time and its nice to have some more stopping power on hand with the flick of the lever if necessary. 

Its great fun though,  learn a PR or FG knot and test them hard - you are only as good as your knot!  no point having the best gear if your knot sucks.

I haven't seen a magic formula. 

There are so many variables in terms of fishing style, depth of water and so forth that you're better off answering the question of how you want to fish, then getting advice on outfits to suit (line, rod length and style, reel capability). 

If you're unsure, there's heaps of good 'how to' info on the Forum, or a decent local fishing store should see you right. Or just ask a question as you've done.

As has been said, you can catch a decent kingie on quality softbait or light lure gear over sand, or catch one on a powerful jig rod near a reef, or on a stick bait set up in the shallows.

It'd be impossible to come up with a formula to explain that, I'd suggest.

Snapper fishing styles veer from straylining with E-glass composite rods, mono and big baits (see the legendary Snappa Geoff's posts) to micro jigging on 10lb braid and long, light graphite rods - and many other styles in between.

That's why a lot of passionate fishos end up with a whole range of rods to suit different styles and locations. Their set ups tend to be chosen to handle the average fish likely to be encountered in their area, with the odd monster or different species bycatch a welcome bonus.

That sounds like a balanced outfit to me. Definitely on the light side for kingfish though. Also, be aware that different manufacturers and even ranges from the same manufacturer vary widely in terms of ratings. There is no substitute for getting your hands on a setup before buying. I'm happy to buy reels mail order based on weight and line capacity, but not rods. Maybe I'm just a fussy bugger, but I've got it wrong too many times!  

this just confuses people in my opinion, I completely ignore breaking strain on braid.

pe0-2 = light

3-6 medium

6-10 heavy

This is all out the window on modern braids though. Breaking strain matters again, in order to compare braids...

Ocea 8:

PE4 = 76lb

PE6 = 113lb