Both Palm and Pocket PC devices offer units that have built-in wifi/bluetooth (or with wireless cards), both have some great security software. You can get an add-on barcode reader, none of the regular PDAs have built-in barcode reader pen or scanner. As for speed, read our reviews on high end units with Xscale or ARM processors. Syncing with central database depends on what your network environment is, what your IT infrastructure is supporting, etc.
I suggest that you read the reviews of high end units on this side which might help you narrow down the search. Based on your check list, iPAQ 5450 comes in mind. It has built-in wifi/bluetooth, and has a bio security built in. There are barcode readers for iPAQs (check Symbol site for barcode add-ons). Read our review of the unit here: