Priming sugar calculators.

[CBMbrewer]

When I put the following info into four different priming sugar calculators I get different answers:
5 gallon ipa at 70*F with a desired co2 concentration of 2.4

Northern Brewer: 5.64oz dme
Brewers Friend: 7oz dme
KotMF: 7.11oz dme
Homebrewing: 5.04oz dme

Which one should I use? Which one do you use? And why are they different?
Also, after I fill and prime my keg should I seal it by pressurizing it with co2 or will this cause the beer to come out slightly more carbonated due to the already present co2 under pressure absorbing into the beer as well as the co2 produced from the priming sugar?

Happy Fourth Everyone!

 

[user 144271]

Why would you use sugar if you have a keg and co2? You can carbonate with just the co2

 

[iAmReynolds]

You do not need to be using priming sugar with a keg. I may be wrong, but will you not end up with clogs in the dip tube or other parts of the beer line.

 

[CBMbrewer]

I have used priming sugar in the past when kegging with much success. No problems with clogging, just a cloudy first pour, then great beer.
The reason I am not force carbing is because I ALWAYS get a carbonic acid bite that I can still taste up to four weeks after kegging. This is even present when I use the set it and forget it method. When I have primed kegs the flavor was not present and have been able to start serving the beer after about 12 days.
Like I said, I have done this with much success in the past, just want to know which calculator is the most accurate and if I should seal with co2.