The 840 Pro is every bit as good as the Vector, and then a bit more. The Vector you linked comes with a 3.5" adapter bracket so that's probably why it costs so much more.
The 840 Evo is a little slower than the 840 Pro, and uses memory that won't last quite as long. But the difference is minimal for regular usage; I'd generally recommend the Evo for best bang for the buck.
Do you think the load times for the gaming drive will be noticeably different between the Pro and EVO?