Cheers. Sticking with 3800x feels right.3900+ needs the X570 board IMO. Even the X470 with it's better VRMs (compared to the B450) isn't at a high enough level where I would be personally happy.
The 3900 running at full chat will put out more heat than a 3800X at full chat and need even better cooling, my guess is this makes it a non starter at any rate.
IMO there's nowhere to save money on this build without compromising its integrity. Lowering the CPU to the 3600 would be an option though as I would be happy using the stock cooler with that chip, even for most professional applications.
Upgrading the motherboard is my last decision now. Feels like a luxury though for the 3800x and perfectly likely I will never is its additional m.2 or pci 4.0
Will be ordering today. Thanks for your help.