Filter for sealed room

I think I need an 8" filter to circulate in my 8x10' room. I only have a 6" filter thats been used and abused and all my fans are already in use.
I need to pick up a combo. Im not planning on using it to exhaust.
Im not sure an 8" is going to be sturdy enough to mount a fan directly onto. Should I just get a 10-12" filter and mount an 8" fan on it, or should I just hang the fan and stand the filter?
Do I actually need a bigger filter than an 8" for the room?

How do I size the proper fan to a filter?
The formula for sizing a room: Length x Width x Height
Divided by 3
Gives minimum recommended fan CFM
Match fan to filter
Ex.) 10ft x 10ft x 20ft = 2000 Cubic Feet
2000 Cu.ft / 3 = 667 CFM
667 CFM fan is Minimum fan size for this size area
after establishing fan size, match it to appropriate sized filter. IE, Can-100

source=http://canfilters.com/faq.html

Thanks for all that info. I was pretty sure I needed the 8" fan, but all the canfilter options were a little much for me.
Im used to the Phresh filters. These cans are heavy duty compared to phresh and will probably be much more stable than the phresh.
The Can100 is quite a bit of coin. Do you happen to know of any comparable brands to these heavy cans?