I'd hate to put it out there and something happens and for whatever reason I'm not able to fix quickly.
That's why I suggested you keep a 2.0 install CD on hand.
Without any package issues, there's really very little to hold you back.
If you've got a recent config.xml backup (which you need anyway) then you've got (2) scenarios:
The best case, you load 2.2.6 2.3 from scratch, reload the backup and you're good to go.
The worst case, the 2.2.6 2.3 install goes pear shaped and you reinstall 2.0 from scratch, reload the backup and your back to where you started.
The worst you get is back to where you are today, but at least you'll learn something about how the hardware responds to a 2.2.6 2.3 install.
Edit
Seeing as 2.3 is now RC (https://forum.pfsense.org/index.php?topic=109076.0) you're better off trying to get the advantages of the latest hardware fixes included w/ a current version of FreeBSD and the code improvements in pfSense 2.3
I've got $0.05 that says you'll have a smooth upgrade if you do a fresh install and restore your config.xml to 2.3 ;)