Thanks, I found the perfect sink after seing Ubergeek63's link to extrusions at Aavid and checking out similar products.
**broken link removed**
Power dissipation isn't much of a problem. Individual devices might have a load of 20-30W, but the duty cycle is very low, so actual long term dissipation would be 1-2W. As well, although there are 6 devices, they are never on at the same time.
I didn't want to use those small clip-ons as I didn't want a device to quickly rise in temp when under load only to have a period of time to cool off. I figured a single large sink would keep temp fluctuations in check.