These dissipate heat from both the front and back. Zip-tying a small aluminum heatsink (chipset sinks anyone?) to the back with some thermal grease, or skipping the zip ties and using a thermal pad would probably allow you to hit 3-3.4GHs with a fan pointed at it. Thing is, you have a limit of 2.2GHs without replacing those resistors, which, if you need more information to figure it out than what the user guide supplies, you really shouldn't be trying to mod them, as you WILL break it if you try.
I've only been able to get 2GH/s without replacing resistors
