I'll tell you right now 8GB isn't possible for a tri channel kit. to get 8GB with three modules one would need to be a 4GB module and the other two would be 2GB modules (for a three module kit) or two 2GB modules and four 1GB modules. In either case they aren't all from one kit. Also most motherboards don't support tri-channel RAM so you would need an x58 system for tri channel capability.
Suggesting you have an x58 system, I would expect the performance to be extremely close between dual channel 1600 and tri channel 1033. There may be a hundredth of a percent drop because the bandwidth of tri 1033 is very slightly lower (compare 25600 maximum theoretical to 24792 maximum theoretical)
In either case it won't be much better than single channel performance because CPUs, unlike GPUs, just refuse to utilize anywhere near the maximum theoretical bandwidth of a memory system.
Memory isn't a bottleneck on any modern CPU except for AMD's LIano series, and even then it's only because of the insane integrated GPU of LIano.