my point is gddr3 is bordering on legacy... and the 5770 is a phenomenal upgrade at a very reasonable price that most likely will add 2 yrs of use to your purchase right out of the box. i still see the 4800 series cards going for ~$500 which, imo is ridiculous. i must say, though the performance on them is absolutely astounding and would be appreciated by any aficionado be he into gaming, image or music editing. when you can't click fast enough to keep the thing working you'll never want to go back!
at any rate, a while back i built a system for a buddy of mine. stats:
cooler master storm sniper case
prudent way superior plus 1000 watt psu with active pfc
amd phenom II quad core 3.2gb 965 black box
his 4890 radeon
4gb kingston ram (he chose a 32 bit os)
msi 790fx gd70 board
lite on blu ray player/lightscribe/dvd burner 52X's LG cd burner (to save on wear on the bluray drive)
2 - 1tb western digital green drives (one for windows, one for linux)
wireless card from walmart (best price, and local) (plus he already had it)
24" samsung 1920x1200 resolution flat screen ($300 cheaper than the competition, great detail and the pc already had more peripheral connections than one would ever need)
bose pc speakers... $60 at sams club and a great alternative to his 2000watt stereo unit he uses most of the time... the bose speakers afford him the ability to hear sound from his pc past 10

m while still not having the cops knock on his door for disturbing the peace.
ati tv wonder 650hd pcie
and his other peripherals... card reader, gaming controllers, etc., etc..
vista ultimate (windows 7 was released like 2 weeks later, argh... dummy... oh, err...)
i can click all day on this thing... and never slow it down. i don't agree with some of the purchases because almost nothing was more than a week or two on the market... which only costs 5x's as much while giving maybe a 2% increase in total performance.
either way... it's your pc. if you want to go with a lesser graphics card it surely should work for you. one thing that bothers me is even the 4800 series ati cards still aren't up to date as they don't support direct-x11. the 5770 is the first ati card that does... so, unless you're going with that or newer from ati you're already getting somewhat outdated hardware. my buddy was kind of peeved immediately when we got his pc together because his card was outdated the day it hit the market (the day he bought it)... and he was already looking to upgrade, but there was nothing to upgrade to.
there's nothing wrong with only getting what you need but i see no reason to spend $70 now and again every 2 years or so when you can get a card that's 2 years newer now for the same overall price. if anything i would get it together and check again on prices for graphics cards. it might just be worth it.
keep in mind... i'm not really trying to push you to buy a more expensive card... just sharing my opinion (maybe i shouldn't come off so pushy then, i know... but that's just how i communicate... it seems that way usually, sorry).
either way, enjoy your new pc... you've made some great choices performance and price wise. starting that bad boy up the first time (once you've installed your os) should be a great experience... i know i'm geeked just thinking about it. all the while i'm typing on my xps m1530... nice system, but getting to be a dinosaur imo.