I can get two titans or two 690s for gaming I have the right specs for both gpus in my computer and don't care about noise heating or price, I only care about fps. What would give me higher fps on single monitor gaming at 1920x1200 with games at max?
quad sli has very little support. you will never get full scaling with the 690 4 way sli. especially not at 1080p. it would provide superior performance in certain titles that are very optimized for sli. games like crysis 3.but i think you would be better off with the 2 way titan sli. full 2 way scaling is very common since 2 way sli is the most commonly used. and with 2 titans you will have some amazing performance on any game. you will have 7.1 billion transistors, 2,500 cuda cores, 6 gb of gddr 5 and 288 gb/s of memory bandwidth per gpu. you need to make sure you have a motherboard that will support run at least pcie 3.0x 8 if sli is enabled. these high bandwidth cards will be bottlenecked by anything lower than that.
The Titan SLI features over 6 GB of memory and over 2000 Cuda cores (now i am talking about 1 titan gpu,now imagine an sli),basically if you have the money,go for it,it will prove useful for many upcoming pc titles for years to come.