I think it depends on what kind of hosting you have, if it's shared, you might run into timeout issues, it might work however for dedicated servers. XCloner can backup sites of any size, the only thing it's dependable of is the hosting limits regarding execution time limits, and of course, how fast they run.
Why not give it a try and see how it goes, and as a suggestion, try creating multiple backups by excluding the large folders and including them in separate ones if you get into timeout issues.
On the xcloner.com site there is a Premium Support area for users, since i am part of the team there, we could help you manage the setup you need.
Regards, Ovidiu