I just had Jim Roseberry build a new PC for me.
Broadwell 6850K (6 core)
64 Gigs of Ram
5 x SSD drives
Video - GTX 970
Many of my productions include multiple sample libraries and many many tracks, plug ins and automation. I decided to put my audio drive on an SSD because a conventional HD wasn't keeping up, so it was either a raid setup or try an SSD.
I also do some audio post and some light video editing, which explains the GTX 970 card.
My old machine was a gaming machine built by Digital Storm. It served extremely me well for 7 years but was no longer powerful enough. This machine is great! And not to be a commercial for Jim Roseberry or anything, but, he did a fantastic job and his support has already been exceptional.
As others in this thread, I would stick with a desktop due to ease of upgrading and changing out parts.