Not many gpu have passive cooling... But my x1900 gt rev.2 isn't even stable at 573MHz and heat was not the problem.
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Intel Core2Duo E6300 1.86Ghz L629A244 @ 3.78GHz
Asus P5K-E Wifi/AP Rev.1.02g
Thermalright Ultra Extreme 120+ FM121 (110 cfm fan)
ATI x1900 GT Rev.2 256mb 513/657
G.Skill 2x1gb Hz--540MHz
CORSAIR CMPSU-1000HX 1000W