I migrated my home install last weekend and am pleased with the results.
Pros so far:
The out of box experience is better for the web filter. I have not had to make special rules to allow things like Netfix apps to work so far like I did with UTM.
I'm leaning the XG interface, I think it is the future of their products. I can't see how they could keep both UTM and XG going forever.
I'm also planning a migration at my workplace and so far in testing the XG performs better on our faster Internet lines. Depending on the speed of your connection it might not matter. I'm seeing a difference with our line that is over 300Mbps, it could just be our specific config though.
Cons:
Having to learn the new interface and rules, some things seem more complex.
My home install runs on a Zotac CL323 and for some reason the XG linked up both Ethernet interfaces at 10Mbps. I had to set them manually to 1000Mbps.
unless you have more than 50 IP addresses I would stick with the UTM. Your comment about netflix is a bit different to a majority of other users who have had to setup special rules to get netflix working.
As far as performance goes I would check your IPS settings. I suspect you don't have many features enabled on the XG.
