There are already a few thread about performances with Oculus Rift ; see Theoritical Performances for a recent one.
Also on AnswerHub, for instance Why is running with Oculus so much slower on GPU
The point is by default quality is set to EPIC so performances are bad if you don’t have a GeForce Titan or at least a GTX 780!
For Oculus Rift, Try reducing supersambling to 140% or 120% with the following console command ;
hmd sp 140
give me 60FPS on Couch Knights on a GTX 750 with very good quality 