I fully agree with Astrobol, the key is to find the correct placement. Once you have done it, there won't be much problem liao.
I personally have 1 x 820, 1 x 620 and 1 x Tunze 6000 in my 3ft. Initially when I wanted to get the Tunze, I was afriad as most bros have bad experience with it in a 3ft.
After a few minutes of twitching, I managed to settle the problem liao. Another bro I know have a 6060 in his 3ft too.