Reliable Motor Fan?

Hi C-Hing,  

Can anyone recommend the most "reliable" and "high-speed" 540/brushless motor fan?

I ask because I have used 5 to 6 Yeah Racing YR Tornado Fans already.  It is very fast but not very reliable.  After a few runs, fan speed slow down without any reason, and it remains slow and need to be replaced.  Several of my YR Tornado seem to suffer the same way on different cars, Touring/FF/F1 etc.  (note I run 6v connection to Fan only).

Any recommendation be appreciated, tks.

you may consider DualSky, quiet and high speed

我都有師兄你的經驗，連續死左兩隻，andy 哥介紹用 dualsky, 暫時效果幾好冇壞

Tks to both C-Hing, looks like I can try DualSky.  From Action Hobby correct.

Other suggestions welcome, tks again.