I was going to attach a 40MM fan to the NB heatsink but no screws I found would do the job.

I picked up an Antec Spot Cool fan at CompUSA for 20% off. It would hover over the heatsink so I guess it'll work, but now I'm wondering which one (NB or SB) it should be used on for the most benefit? I'm running out of room to put stuff so I'm not sure I'd go back for another one even if it does a great job...