You will gain a large performance boost as the old sata interface will only bottleneck sequential transfer speeds when what makes a ssd feel fast is the random read speed and memory controller.
Get a 780... watching this comparison between 780 sli and Titan sli is almost painful. Just think of the people that dropped $2,000 on two Titans.... The cheaper cards should never beat the more expensive ones 9 times out of 10. Unfortunately, Linus tends to exaggerate the importance of large amounts of video RAM. In fact, there's still not much of a gap between the 780 and the Titan when running at 5760x1080.
Do not buy kits. There are various reasons for this. I should start off by saying there is nothing bad with a kit. It will work properly and would will have a loop by the end of it. However, in kits the parts you get are typically low-end. I would never recommend a non-laing pump for a loop. Laing pumps are known for being quiet and reliable working for years without any issues. This is just an example. Kits tend to have lower quality everything. Secondly when buying a kit you will not be able to prioritise what you want in a loop. Maybe you are focusing on performance, maybe on looks? A kit will not give you this choice.
Most importantly a kit will not let you learn. Believe me when I say water cooling is a big investment, not only of money but also of time. If you feel that taking your time to look up components and make a parts list and doing research is something you would rather not do then you will be in for a shock later on. If you ever have a problem with your loop you will be much better placed after you have done your research and after selecting your own parts.
Therefore I advise you to go to the two stickys HERE and HERE and spend time reading about watercooling, then make a parts list and draw a diagram of what your loop is going to be, then ask us to review your parts and let you know what we think of the parts you have chosen.
