Just a tip so people may save time and efforts. I am on 4.3.12, using 5.0 RC1 guest addons for some VMs like windows 10 (works OK, even shared folders and mini tool-bar and seamless). NO other later build has worked for me. I even tried out (saturday) 5.0 RC1.
On 4.3.12 ALL VMs, and I mean TEN (10) different Linxues, FOUR (4) Windows (2000, XP, 8.1 and 10b130) and TWO BSD work OK.
My only "maybe" is that I have a nforce networking controller (NAT works OK on 4.3.12) but maybe vbox guys should solve that, there are a LOT of PC's with nforce....
I just hope VBox 4.3.12 works on Windows 10 stable. I will be migrating windows machines directly from 7 to 10 (no 8/8.1 for me no thanks)
Just my 10 cents