I would think they all produce the same since they all use the same chip at the same clockspeeds. The only difference will be with the quantity of memory where the 256Mb versions will produce more heat.
I have the Gainward FX5900. The highest I've seen the temperature go during the middle of playing SWG at near max detail setting and running at the "Enhanced Mode" settings(Ultra like speeds) is 49 degrees C. Whats great about this card is that at those overclocked Ultra speeds(440 core and 900 memory) you still are within the manufacturers warranty. Then if you want, you can press the auto detect button and it will automatically configure the card for its maximum safe settings. I did this just to see what speeds it came up with. 480 Mhz core clock and 980 Mhz memory clock. I suggest you get the Gainward card. Not only is its performance outstanding, it also looks cool as hell to boot with dual blue LEDs on the fans. I wish I had a clear side panel. Besides SWG I can run every other game I have on max detail settings with no slow down. With SWG the only thing I don't have at max is shadows and global draw distance. I can turn the draw distance on and keep respectable framerates until I go into a city. Thats how powerful this card is. If you're an extreme overclocker and you have a side fan blowing directly on the card, I'd say hit that autodetect button and go to the max with the card. I'm thinking of installing such a fan. BTW, my temps are with 5 case fans. If you only have one or two, you might get higher temps.