The 45-90 and the 458 WM are kissing cousins for all intents and purposes with almost identical case capacities so you can use 458 WM reloading data... AS LONG AS YOU KEEP THE PRESSURES WITHIN THE CAPACITY OF THE NEF FRAME......I'm almost afraid to post that information to keep someone from using the 458 WM max data and getting hurt.
Whether or not you need to throat depends on the bullet weight and shape you want to use. RN's and WFN bullets are shorter and hit the lands quicker so the bullet is seated deeper in the case...the pointy ones can get away with longer COAL's, seated less deep which will gain you more powder room.
I think the 45-90 is the best "compromise" between case size, bullet weight, velocity and recoil, for me at least. You can still shoot the heavies, 600 plus gr bullets at much higher velocities than in the 45-70 AND you can shoot the lighter and midweights and MUCH higher velocities than the -70 so get much more smack for your buck. I shoot more -90 cases with 450 gr plus/minus 25 gr in my 45-120 than the larger -120 case and 720 gr T-Thumpers. A 450 gr slug seems to hit the magic place of higher velocity/striking energy compared to a 405 gr or 525, but that could also just be the load I worked up.
For those who want to bother checking and contemplating...a slightly lighter bullet, i.e., 450 gr compared to a 500-525 gr, at a higher velocity "might" give you a higher striking energy at the ranges you are shooting and all the penetration you need ...you just have to let your fingers do the walking through the ballistics tables.
Luck
