What you need to do if flash back to your WM5 ROM, copy your pim.vol back to the device (I think you also have to soft reset to get it to read it), then go
here and follow the instructions on how to get a free mail2web push email account.
Once all your contacts and your calender is synced with mail2web, you can now re-flash your 6700 to the WM6 ROM.
The last step you need to do is start from step 3 in the post linked to above to sync your 6700 to the mail2web server.
You should now have all your contacts and your calender back.