It really depends on which shaders dude, I can run Normalers at 40+ FPS on highest settings with my GTX660. I can run Chocapics V3 Ultra at 60+FPS with everything else on medium. I have owned both Nvidia and Radeon cards and I HONESTLY have to say that Radeon cards are better with Minecraft. I don't know why, but they just have worked better in my opinion. Maybe go for a Radeon 7870 or a 7950. If you have your heart set on a Nvidia card, then go with the 670. Most games are optimised for Nvidia cards, so if you plan on doing lots of gaming besides Minecraft, then a Nvidia card is the way to go. But if you know ANYTHING about computers at all, make sure your power supply is sufficient other wise your whole system will just fart and die on you (trust me, I've been there). On another note is make sure your computers case is big enough, because anything better that a 650ti gets pretty long.
SOURCES:
Me, I built my own computer. View my build here:
http://pcpartpicker.com/b/F6h