To me I think this is the best build for [Burston Prime] with a Viral + Slash Build. I've did a lot of testing and researching which gave me theses results:

Build Info:
With this build your able to proc Viral and Slash decently with added damage to Slash with Viral (Of course), CD, and Damage with [Serration], VS, and (my) Riven with Damage & CD. Because of aditional CC with P.S and the Riven, Mutlishot with S.C, and Hunter Munitions, your able to proc Slash decently of 10-18 in 4 - 7 burst.

I choose to go with one dual stat mod and Prime [Cryo Rounds] then two because with further testing and the recent status changes, Viral stacks up to a max of 10, even though its great to have more SC to proc more slash, its only a small amount more with 2 D.S.M and with a multishot of 1.9 it helps out, so I opted for P.R.C to deal more damage and proc viral more, if you like you could switch it back too 2 D.S.M for more consistency if you want.

Also Vigilante Supplies, it gives a 10% chance to increase the power of a crit hit which can come in handy. I recommend doing head-shots to further increase slash damage overall.

Added: With the new arcane slot on primaries and Galvanzied Chamber and Aptitude you can further increase the damage to 246k consistently, I went with these mods and arcane because I run this gun along side [Ash] and with my build I can stay invisible increasing my damage with melee kills. And I find this to be more consistent without running [Galvanized Scope] because since I run this on [Ash] I aim to do damage overtime and getting headshots consistently for me is kinda hard since I play on PS4.

Personal Note:
I love the [Burston Prime] so much it was my first gun I earned in the game and came to love further down the road, I just saw people weren't using this as much which sucks cause its great but hey the more people don't use it the more higher the disposition it will get XD. Being a veteran thats starting to get back into the game after 4 years, I believe a lot of weapons can be great if you take the time to build it correctly, so if their any lovers of Burston Prime who want a great build for End-Game, I think you should try this out, it might surprise you.