Suggestions on Updating My HTPC for Gaming

I used Assassin's guide to build an HTPC about a year ago. Here's the relevant info for the current build:

CPU: Intel i3-2105 CPU 3.1 GHZ
RAM: 8GB Ripsaw DDR3
HDD: SAMSUNG HD 240UI 2TBx2 (Ecogreen)
Mobo: ASRock H67M-ITX LGA 1155
Case: nMEDIAPC HTPC 5000B Micro ATX Media Center
PSU: Rosewill Green Series RG430-S12 430W Continuous

I've been thinking about upgrading to a new video card and possibly a new PSU as I'd like some more oomph for gaming. I'd like to get more out of Steam, play the new Tribes game as I was an addict of the original series, and generally be able to play most games with a nice presentation. I don't necessarily want to play the most cutting edge FPS's in 1080p with everything set to high, but I would like to be able to play most games with a nice presentation (I'd like to play things like Rayman in 1080p though). As of now, I can't even get FTL to run properly.

So given the above information, what would be the most cost-effective upgrades to the system as it stands? I asked a few people on Reddit and got suggestions of the Radeon HD7750/7770. I'm having a tough time getting a good idea of what I'd get with the 7750: I understand it has low power needs so I don't have to upgrade the PSU, but the reviews don't really describe what my gaming experience would be like.

In looking at other cars, too, i'm not even sure what will fit in my case/mobo. Basically I'm just lost in general trying to figure out how best to upgrade my system. Any help would be much appreciated!

I think I've ended up deciding on the 7750 here: http://www.newegg.com/Product/Product.aspx?Item=N82E16814127709.

Is the only way to figure out my space to pop open my case and take a look-see? I don't have anything else installed aside from what's listed above, and the nMedia case I have is pretty large.

Yeah? One of the reasons I went with the 7750 was that I figured the PSU could handle it. I had planned on spending in the $200+ or so range for a card and PSU if need be. I figure from everything I'm reading, Corsair is the brand to go for. But this was my first build in about a decade, so I figured it was best to stick closely to Assassin's recommendations, and he didn't have bad things to say about the Rosewill. I figure since I'm going with the 7750, I'll stick with the rosewill for now, but assume a 500w-ish Corsair would be a smart upgrade at some time in the future?

Thanks for the recommend of Tech Power up. I like the layout. I've spent way too much time on Anandtech and Toms trying to figure out which card I should get, there's just so many stats to compare. That's initially what confused me about the 7750: People on reddit were recommending it, but sites like Toms were saying that it wasn't really much for gaming/wasn't much of an upgrade over integrated graphics. So I was initially hesitant, I mean... we are all spending time/money making HTPCs so we want everything to look nice. I don't want to spend any money for a game card if everything has to be super low res in order to play.

But have you ever seen this site: http://www.game-debate.com/. I had never heard of it before, but it lets you put in your hardware specs and then you can search for random games to see if they will run on low/med/high graphics. Pretty much everything I had been planning on playing looked to work under recommended settings. Is this site trustworthy for that kind of info?

I mean, ideal world would be everything 1080p, world peace, etc. But I watch most TV in 720 and movies as well... So I'm fine with 720p gaming.

That being said, though, I was looking at Passmark video card rankings, and noticed that the Geforce 650 ti is ranked abovethe 7750, 7770, and the regular geforce 650. It requires a 400 psu and is the same size as the 7750, so it would work in my setup. I found one for $159 (EVGA on newegg). Should I go for that, or does my CPU limit the performance gains I'd be getting as I move up the scale in cards?

EDIT: Unless anyone has a reason that I shouldn't, I think I'm going to go with the EGVA 650ti. It comes with Assassin's Creed 3, which I had planned on getting anyway, and that makes it's price come down into the range of the 7750 I was thinking of getting. Let me know your thoughts, all, and thanks for the input so far.
Edited by Effingood - 11/15/12 at 5:57am

Alright, the 650 ti has been ordered. I probably won't install it until I have a little bit more time in December, but thanks for everyone's input.

Also, YRD: I just noticed you're from Elkton. I grew up in Easton, MD, and used to have a good friend that lived in Elkton so I spent a good deal of my formative years hanging out there. Small world.