What FortiOS to choose? 4.3, 5.0 or 5.2?

I have several FortiGate 80c and they are all at 4.3.15.

I remember few years ago when 5.0 was first released, it suffered performance issue and that's why I stick to 4.3.

However, I think there's a bug related to VPN in 4.3.15.  Unfortunately, 4.3 is no longer supported by FortiNet so I think I might need to jump to version 5.  So let me ask this stupid question:

Is there a general consensus about performance in 5.0 and 5.2?  I've seen some recent posts about 5.2 -- it might be a better idea to stick to version 5.0, right?  Is there a version that most people would agree on its quality as very stable?

Thanks in advance.