On an X201, if you're expecting to keep it in that system long term and not move it to a faster machine, the speed advantage of the 840 Pro over the regular 840 is going to be lost and you're better off saving the money.

Overall, they're very good drives; I've got a 512gb 840 Pro (and an OCZ Vertex 3) in my laptop right now, and they're what my employer has been buying for laptops lately because of supply shortages on the Intel 520 480gb drives. We're probably not going back to the Intels; the Samsungs are faster.

My only complaint with the same Samsungs are a little on the pricy side, and they are a little worse than other models about lose write performance when they fill up completely (although using trim, and making sure you have some empty space, should keep this from being noticeable for most users. It's been problematic in DB servers.)