Get the GTX 650 2GB. You didnt mention on what resolution will you play. @ 1080p i guess you can game decently @ mediu/high, sometimes ultra (with all the frame killer settings off, like MSAA etc). Your case will be sufficient 99%
Just a small advice: on the road, add a custom cooler to the FX 6300, because the stock cooler tends to be loud and with an aftermarket cooler you can OC your CPU to a more decent 4,3 - 4,5GHz.
I dont think that you can find a new Radeon 5870 on the market nowdays ^^, and between the Radeon 7770 (did not mention 1 or 2GB) and the GTX 650 2GB, performance wise they are on paar ^^, the choice can be made purely subjective ^^ ("i like nVidia more than Ati/AMD" or vice versa).
Not purely subjective, the 7770 is performs around the level of a 6850, the 650 is barely more powerful than the 550 Ti which the 7770 whoops
The 650 is more on the level of a 7750, you can like Nvidia all you like (I've used them exclusively but a better card is still a better card ), but I wouldn't recommend an inferior product, especially since even little performance differences mean alot for budget cards
Roland, i dont want to get into a polemic with you i am no fanboy (as you can see in my sig i own a Radeon 7850). Yes, the 7770 has the edge against the "simple" gtx650". The real world performance difference is minimal, especially if you take into account that the article you linked is 15months old (yes, you can make a good idea about those cards from it), but i can see in some titles this conclusion (radeon 7770 - 42,1 FPS, gtx 650 - 42,1 fps), yes in AMD optimised games the Radeon is better.
Anyway, to much talking.
Personally, i would squiesse a bit more money out and get the "new" R7 260x (or the non x), or atleast get the 7790 or gtx 650ti.
Yeah I know, things tend to get heated in forums sometimes , I didn't actually mean to call you a fanboy (and I apologize if you took it as such), it's just that the 650 is really not worth it unless you really want shadowplay xD, every extra frame for a lower end offering helps
I'm assuming that op is based in India by how he refers to the case as cabinet so that'd usually mean a tighter budget
Yeah it's an old article, both sides have updated their drivers many times over so both ends will have slightly better performance by now, it's just that Nvidia has had a history of rather meh lower end offerings after phasing out the 9800 series of cards
A card in the class of the 7790/260x range will be fine for smooth gaming at medium-high settings for a while, and the FX 6300 should last you till another GPU upgrade cycle
Another thing I forgot to mention, that CPU is not compatible with that motherboard, you should get a 970 or 990FX mobo since the B75 mobo is for Sandy and Ivy Bridge Intel CPUs
Also if your budget allows for it, a total of 8GB of RAM would be ideal (if your budget is tight right now stick with one stick of 4GB DDR3 and add another later on)
If you are in India (and forgive me if I'm wrong), you should get this motherboard instead, though you're not really going to be overclocking well with it (from what I've read, it doesn't have sufficient cooling for the VRMs so overclocking wouldn't be a great idea with this board)