Bathroom vent fan...too big?

[spudmunkey]

So, we want/need to install a ceiling vent fan in our bathroom. We've both had serious mold problems in previous homes without them, and we're thinking we want to "upgrade" to a larger CFM-rated fan than what it recommended. Is it worth it? Would a larger-capacity fan actually work better in a small space?

The bathroom is 8wx5lx8h.

Conventional wisdom would suggest a 40-50 CFM model, but we were thinking about a 70-80CFM, if not a 100-110.

Any thoughts? The bathroom is on the edge of the house, and the roof has a very shallow slope, so the fan will need to be off-center in the room, closer to the interior of the home (if that makes a difference, so it'll be about 4ft from the exterior wall.
edit: Yes, absolutely. I've already picked-out the Lutron timer switch thing. Thanks for the tip!

http://www.amazon.com/Lutron-MA-T51-WH-Maestro-Countdown-Timer/dp/B001EFV1DA/ref=pd_bxgy_hi_img_b

 

[MM]

I would upgrade to at least 70 cfm, but the problem is not with the size of the fan necessarily, but that it doesn't run long enough. For instance, 5 minutes after a shower you leave the bath and turn off the fan but the humidity is still there. You can buy timer switches that will allow the fan to run up to 20 min. or so after you've left the bath to exhaust the humidity.