keerym,
check with your dealer.  Many have been already and will show you info.  
I did look at GT/GX replacement, but only briefly. Unfortunately it appears not to be a return to old 318 supremacy.  The frames are ~3.x mm vs the 4.xmm of old 318s, current X series, and new X700s.  So won't be moving the boat with it.
On plus side, I think it still had diff lock, and now offers HDAP tires.  No 4wd though, so still needs chains.  I think a little more HP, biggest deck was around 54", and new seat with built in grab handles.
Again, I personaly think dealers are one of Deere's advantages over competition, especialy on consumer equipment end, so pay them a visit.  Then perhaps you can give a better update than this!  In meantime, sorry for not more detail.