I'm going from memory here...
The 330 has a graph for a display to show you roughly where you're at in the combustion scale (too rich, too lean etc). Also you can hook it up to a computer and download the readings also.
Aside from that I think they are basically the same unit. I have the 327 and I really like it. I do wish I had the computer abilities of the 330, but I can get around it for now.