I am using currently a 20mp Sony RX10III and my PC has no problems with the files nor Photoshop or LR.
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My PC -is- getting long in the tooth though here is a paste of the specs. Do you think it will handle D850 files being 2.5x larger (roughly) than the 20mp Sony's?
Your i5-760 is not a superfast CPU but not too bad, either. 8GB of memory will be just fine. The one info I can't get from your specs is whether your C: drive is a hard disk or an SSD. The latter will speed up almost everything you do on that computer by a substantial margin.
Much of what LR and PS do doesn't care about how large the image is. When you work on details of your image, these programs show you only that part of the image that fits on the screen anyway, so 20MP or 45MP makes no difference. Where it does make a difference is in load times (some), save times (more) and in the application of any changes that are global to the image. LR/PS, in their latest incarnations, make use of graphics card horsepower, but from what I read about it, that's still limited to a relatively small number of conversions.
My advice: if you don't have an SSD in the system yet, get one and keep the PC. You'll be more happy with it processing 45MP files than you were before with the much smaller ones.
If you already have an SSD in it, either follow mikew's advice or, if you'd like to get more accurate, scale a series of your 20MP pics up to 45MP in PS, somewhere near the D850's 8,256×5,504 native resolution, and then process them the way you usually would. That'll give you a feel for what to expect.