Well, I could probably make it fit in the case (it's not THAT small), but that's a fair point.
I have an Antec 900 and an HD4850 is almost long enough to render the top 3.5" drive cage unusable. The cage itself would have to be removed to fit a 5870.
Unfortunately, I also want to overclock it (not right away; I just want the option to be there when I need it), and I heard the only ones that had an unlocked BIOS were ASUS, Gigabyte, and msi. The one I'm looking at right now is out of stock. I do hope a miracle happens and the price just spontaneously decides to go down while they're restocking. Of course, I heard that you can do a BIOS flash on whichever one you get, to change it into ASUS or whatever you want, but I quite frankly don't wanna mess with something that has even a small chance to brick the card.
You're thinking about unlocking the disabled stream processors, not overclocking. Overclocking is pretty easy, and you might be able to come close to HD5870 levels. Unlocking requires a BIOS flash, an act which might brick your card, and even if it does succeed, you might find that the disabled components were faulty. There's also the issue with the smaller cooler on the HD5850 - you might actually have to drop the clock speeds to get it to run stably if you manage to unlock the stream processors. This isn't like some of the older video cards, where an unlock could carry a huge performance boost.
he wouldn't need to remove the fan shroud to fit a 5870, I have a 5870 in my antec 900 and it fits like a glove. And also, for cooling solutions, the best temp drop per $ is found here:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835103065&Tpk=Coolermaster%20212I personally have the TX3, the cheaper version, but the 212 is worth the upgrade. Your specs are going to be really similar to mine (besides clockspeeds)
My two rigs:
Antec 900s
5870 in 1, 5850s in xfire in the other all 3 OC'd to 1000MHz core/1200MHz mem (1325mhz mem on the 5870)
Core i5 750s, one at 4GHz on air w/ the 5870, soon to be on a corsair H50:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835181010&Tpk=Corsair%20H50 and another i5 750 @ 4.62 GHz on a corsair H50 24/7.
The Coolermaster 212+ would allow you to overclock if you need to, and would keep your CPU within tolerance on a warm (100F+) summer day at stock, where the stock cooler fails. Also- when applying the paste to the coolermaster, be sure to spread a fair amount between the heatpipes (you'll see what I mean if you get it) and a small dot the size of a pea on the CPU itself, then attach it. This is what I've found is the best way to apply (my TX3, the smaller version with a smaller less powerful fan is keeping my CPU @ 60c at 4GHz)
And btw, the differences between a STOCK 5850 and a STOCK 5870 can be between 20-25%, the differences between an OC'd 5850 and a 5870, are roughly 3-5%. That said, the 5850 should be PLENTY for anyone but an enthusiast's needs. Neither of my XFX 5850s have had any cooling troubles. the only ones I know of that have trouble are some 5770s that have coolers that don't do anything for the VRMs. my 5850s @ 1000/1200 have never gone above 70c (Furmark at its most intense settings and 2560x1600) and doesn't go above 50c in 99% of games with a custom fan profile in MSI Afterburner (best OCing app to date, imo)
sorry for a bit of a lengthy post here, feel free to PM me if anything is unclear/off as its 1:30am for me right now and I just got done doing a lot of repetitive benching for a contest w/ some friends =P