There is no danger of me buying a 64-bit Radeon. Or a 13487-bit Radeon. Or any Radeon. :-?
Seriously now, the graphics card universe divides into three parts.
1: Entry-level, in Oz dollars, about $100, typically $70 to $150. Acounts for roughly 85-95% of all sales. Gforce 4MX, Gforce 4000, FX5200 and etc.
2: Mid-range: around $300, typically $250 to $350. Accounts for 5 to 10% of all sales. FX5700 and similar.
3: High end: FX5900 and up. Practically no-one buys them. If you think that's just me, think again. Ask your wholesaler how many they move. Better yet, ask if he has one in stock. You can order 30pcs of FX5200 and they will ship within the hour (because they have 50 or 100 or 1000 in stock), You can order 2 x FX5700 and they will ship within the hour (because they have 5 or 10 or 20 in stock). Order one of anything in the $500+ price range, and you have no more than a 50/50 chnce of getting an immediate shipment — and I'm not talking hole in the corner disributors here, I'm talking good sized wholesalers with 10 or 20 staff of the payroll.
Calling an FX5900 "midrange" is ludicrous.