There are many variables.
-- one simple rule of thumb, a good starting point, is to size the bullet 0.002" over groove diameter and the nose 0.001" over bore diameter. Seat out until the nose engraves slightly.
-- another rule of thumb is to size the body of the bullet to result in 0.002" - 0.004" clearance at the chamber neck. Any tighter than 0.002" clearance will likely result in difficult chambering. Sometimes this neck clearance is the one that matters, other times the neck clearance can be very sloppy and the gun will still shoot well. Note I said "neck," not "throat" or "freebore."
-- it's a toss-up which bullet design will shoot best in a long freebore. The temptation is to fill up that freebore with a fat front band (or bands), but the benefits of a snug fit may be offset by increased distortion when the oversize front band engraves. Also, as a practical matter, you'll need 0.002" clearance in the freebore to ensure reliable chambering. A 0.287" X 0.320" front band in a 0.287" X 0.320" freebore will be asking for chambering problems. More likely the front band would either have to be 0.285" for reliable chambering, or else use a much shorter front band.
-- at the end of the day, the only way to determine the optimal bullet diameter is to experiment with different diameters. If you order a 0.287" bullet, you can always size it down to 0.285" or so if it shoots better at that size.
Re: the RCBS 168. the photo at the RCBS website shows what appears to be a bore rider. Ditto their photo of the 145. What do the noses of your bullets actually measure ?
What does the nose of your NOE bullet measure ?
How much clearance does the cartridge have in the chamber neck when a 0.284" bullet is loaded ?
What is your bore (not groove) diameter ?
I've shot 1000's of cast in the 7TCU, deep seated with bullet lube exposed to the powder space, and accuracy was generally 2 MOA - 4 MOA, depending on the load, in a 10" TC with standard sights. The load that I settled on for IHMSA was 2.5 MOA, if I remember correctly. But that barrel had a pretty ordinary throat, not super long freebore like yours. I was shooting a 170 gr. NEI bore rider designed for the Mauser, but the nose was way too fat to be a slip fit in a TC, so I just seated it deep. That fat-nose bullet shoots sub MOA in a 7/30 Water TC carbine, and it actually prefers to be seated deep so that it has to jump to the rifling.