kamikaasie in 4890 vaporX review thread said:but my pc case is very cool but noisy
2x 25cm front and side
2x 12 cm out back and psu
fan set on memory dominator
zalman copper on processor
if i say temps 67 and 71 fullload hd2900xt crossfire,1 had an artic cooling triplefan (standard 2 heatpipes was first type was to hot to), that was 67 but the fans almost never go rotate only auto at 70 degrees,other was a new type standard with 3 heatpipes-15degrees less then 1th in begin, so i think you can see my case is very cool for that card i think.
but something is right here its an open cooler also, so not all heat go out, also a lot heat come in pc case, they claim its produced so it go out, but it always will go out ofcourse ;-)
so thats the point for now all run hot on idle because fan go to slow,under 1000 on start point, but when go to power mode its also very loud .and it also blow lot VERY HOT AIR in the pc case.
so my opinion , the cooler looks greater then the funtion it have.
maybe they look to much to try win performance but better win in less power and less heat also .
so for my opinion i think the cooler vapor-x as better cooling isnt a well done job.
also not the noise from the fan , thats also more at 40% then the xfx4870 s in crossfire on 60%
my card is 53 degrees now stock but the memory is 64 , so your temps indication are right if not look at the memory
my temps are ok then but memory go 10a15 higher look in everest it gave 3 temps 53gpu 64mem 51environment
also the clocks of memory not go back in idle mode only core go to 240.
So if I understand you correctly, you have this:

Golden rule of air cooling is always have more outtake than intake. So I'd suggest trying to turn around the 25mm side panel cooler and see if it decreases temperatures. It looks like the air is trapped between and under the cards, creating 'hotspots' which are also associated with having more intake than outtake.