Minimum version of SmartGWT that works with GWT 2.7?

Hi, I was wondering which version of SmartGWT is the lowest one that works 100% with GWT 2.7.

Our current version is 4.0, and I would like the make the most minimum upgrade to get it to work with the newest version of GWT.

I would upgrade to the latest 5.x version but I noticed many incompatibilities with our existing code and we don't have much time to patch these issues up.

Thanks!