Windows 7: Windows ReadyBoost help

Hi everyone,
I have a 4gb usb flash drive, and I decided to use it for ReadyBoost. But I have a few questions.
Which format should I use: NTFS, FAT, FAT32 or exFAT. I heard ReadyBoost in Windows7 supports exFAT. What allocation unit size to choose (ranging from 512 bytes to 32768 kilobytes in exFAT). What is the difference in unit sizes. And which option should I choose in ReadyBoost: Use this device or Dedicate this device to ReadyBoost. Thanks in advance.

I formatted mine for NTFS using default unit size.

I agree

If you choose "dedicate this device" then it will use all the space. I have an 8 GB USB key and just for grins I looked in the ReadyBoost options. If I selected "use" instead of dedicate then it would take 1/2 my storage and leave the other 4 GB to copy files etc..

Runs fine without it and it's a secondary machine so I see no point of having my USB key sticking out of it when I could use it for other stuff, like disaster recovery boot utility.