This is quite difficult to answer. Depending on your hardware configuration for on-premise, you could have better or worse performance than SaaS. We have recently moved from a hosted solution to SaaS, in some areas we improved performance and in others we lost a little in performance. But when we migrated we upgraded to 14.3, converted reports to JasperSoft, and had to remove triggers and other components that were not supported by SaaS.
There are benefits and drawbacks to both solutions. I would not base my decision to move solely on performance. Remember a lot of CA PPM performance issues are not H/W related but configuration/customization related (Audit, Attribute value protection, heavy customization's, poorly designed process/scripts/queries, etc).
Personally I can argue for both on-premise and SaaS (I like both). To select what is appropriate in a particular case I would want to know what the customer objective is for CA PPM now, 2 years, and 5 years down the road, functions they will use in CA PPM, user base size, etc.