Just a quick note to make sure you have a 64 bit OS if you're going with 8 gigs of ram, otherwise a bit more than half is wasted.
I'm not the expert like a lot of people here are, but that looks like a nice build to me. Very nice. You should take a look at the benchmarks on the i5 2500k, you honestly probably dont need to overclock. It's just fine (way more than fine) for gaming completely stock.
I just built my PC and it has very similar parts. The only things I used differently were the PSU, GPU, SSD and Case, but even those are similar. For the PSU I went with the XFX XXX 650W since it was on sale for $65 AR (and still is on Newegg) which is ridiculous deal for that PSU. The case I went with was the Antec 300 like you mentioned you want. It has been great, and if you are willing to buy elsewhere, you may want to shop around for a place where it is in stock (amazon?). The SSD is the only thing I would recommend a change on rather than just giving you an alternative. I suggest going with something from the Corsair Force series as they perform better in almost all tests or waiting for the Vertex 3. I also mentioned I had a different GPU, but that was just an issue of me not wanting to play games on my system (it was built for video editing).
The size of the monitor is immaterial, it is the number of pixels that the video card has to manage that counts.
A 23" monitor may be 1080P(1920 x 1080) or somewhat less. If the monitor was a 55" unit, it would still be 1080P and use the same video card.
More than 1gb ram on a video card is mostly marketing when used with a 1080P monitor, 2gb may be of value on a 2560 x 1600 monitor.
I like the card you picked, XFX is a good supplier. I also like the direct exhaust stock cooler. Don't sweat minor differences.