The thing I don't understand is this, 'PL-259 Connectors are not recomended for use above 300Mhz (See N Male options).'
One thing others haven't mentioned (something to remember when talking about RG-8 coax) is that RG-8X or Mini-8 coax (smaller diameter, about 1/4 - 1/3") is no where the same as standard RG-8 (about 1/2" diameter) in performance or loss numbers. RG-8X was designed for HF use and works well there, but has way too much loss for VHF or UHF use. While it may "work", it won't "work well" except for very short runs.
"N" connectors are a bit less lossy than the typical "UHF (aka PL-259/SO-239" connector, but that's really not what you should be worrying about. What you need on your coax is what you need to directly connect to on each end of the coax. Remember that it's perfectly fine to have different types on each end of your coax if that's what's required. The loss difference between "N" and "UHF" is only important if you can completely control what they connect to.
Most often a discone antenna will need a PL-259 on that end of the coax or you'll need an adapter to make it work. An adapter will have much more loss than any difference between a properly installed PL-259 and a properly installed N connector so you should go with a PL-259 on that end of the coax (if your antenna has a different connector requirement then by all means make the appropriate substitution).
Most often a scanner will have a BNC connector (they also often come with SMA so it pays to verify) so a BNC on the scanner end would provide the lowest loss. Note, if you have an SMA, a short jumper will probably be necessary since the SMA is such a small connector the LMR-400 will strain the connection if directly connected). If you use the jumper, it may be good to have that jumper premade with an appropriate SMA on one end and an "N" on the other end. Your coax should have the appropriate "N" on it so no adapters or barrel connectors are necessary (e.g. if the jumper has a male "N" have them put a female "N" on your coax).
As you can see from this, you will probably need different connectors on the ends of your coax. Your lightning arrestor should also be factored in and that may call for other type of connector as well, depending on what specific one you purchase (a good place for those low-loss "N" connectors if you haven't yet purchased it).
You want to avoid having to do what was needed in my situation going from a Mini-UHF male to a BNC male when my needs were immediate and supplier's selection was limited. I had to use a male-BNC to male-BNC barrel connector, a male-mini-UHF to female, and a female-mini-UHF to mini-female-UHF barrel connector. While it did the job at the time, it wasn't very efficient and made the connection an extra 3" long.