The 840 Pro is faster and has a longer life span. It uses SLC instead of MLC which again is reliability. I currently have the 840 non pro mainly because it is still very fast compared to my old HDD, saved me about $50 at the time, and by the time it dies SSDs will be MUCH cheaper and faster/more reliable etc. Most people will say spend the extra money for the pro, I do agree for most cases but it really depends on your personal preference.
Well, just about any SSD is going to be a magnitude faster than your standard disk harddrive, and in all actuality you'd probably have issues trying to differentiate real-world performance between SSDs.
The Samsung 840 Pro is a really good SSD that benchmarks well, and is considered very reliable (the scary thing about SSDs!) since it uses its own type of controller, as opposed to the dime-a-dozon SandForce. (I think there are only a couple other brands that use their own types of controllers; I know Crucial and OCZ are among them.) In other words, there is a reason you're paying that premium, and it's not just because it's a name brand.
I, personally, own a G.Skill Phoenix III (240gb), which uses a SandForce-type controller. I think it retails for around $180 bucks, but I managed to snag it for $150, which is part of the reason I got it other than I have and use G.skill memory. I have had it for about eight months now, with no complaints. I know I don't have a top-tier product, but my computer still boots up quick, along with any other application or game. I am just happy to have improved productivity.
But, uh, the core of my rig is about $550. You've almost spent thrice that. I think I would just go with the Samsung 840 Pro, but get a 256gb instead. (Will 128gb be enough for you?) An extra $70 bucks is a drop in the bucket.