Unless it is a terrible brand a 700w PSU should be fine. I wouldn't recommend that card however as it is overkill for for a 20" monitor and overpriced in general. You can get an HD4890 for significantly less and it will perform similarly.
Almost all 20" monitors are 1600x900 though and for that resolution an HD5770 should be excellent. It is about $160, DX11 and very cool/power efficient. It is approximately 50% more powerful than your 9800GT.
i guess im wondering the same. im really stuck on getting the 275 as well.
my specs are
Dell inspiron 530s
Intel Core 2 Duo CPU E7200@ 2.53 GHz
installed phys memory: 2 GB.
2 monitors: view sonic VP2030b 1600x1200. Dell E207WFP 1680x1050
currently have (laugh & cry) ATI Radeon Pro HD 2400
windows vista, and i play wow A LOT. ive been in 10m TOC and i get 5 FPS. and itll STOP sometimes. GGRRR.
i was in chat on WoW and asked about the 275; positive feedback. they suggested get the basic & overclock it myself, but one dude recommeneded liquid cooled cuz of a $100 premium on the difference of the basic 275 vs one cooled & overclocked. idk if im alright w/ puttin liquid or payin more for something that doesnt really need it. wouldnt a couple fans do fine? and how much is good enough on the over clocking if i only have the card for say a few years?