Hmmmm, interesting one.
The early witness is a far better gun than the X-Five, the later ones suffer on quality (on the magazine more than the gun).
The GSG-92 is fine but if you have an X-Five theres little point in buying one, apart from the looks (and these are Cybergun guns so the finish will wear quickly) there is little in it.
If you are buying one to buy another airgun then do not waste your time with either, if your buying one because you have a genuine interest in firearms then go with whichever you appreciate the most. Remember the GSG92 is not a replica of the Beretta 92, its a replica of a Taurus PT92 (note the safety\decocker is in the original position yet the GSG-92 retains the more modern trigger guard and magazine release position).
Great Deals with : Dave Dee, Dozy, Beaky, Mick & Tich