I know that the sights are different from the A2 and A1 uppers but what if any are the other differences.  Also are the older A1 uppers any different than the current production ones like the DPMS "Panther Light"

Any info would be great!

It depends on which version of the A1 upper you get.
There is the version that is like the original M16, no brass deflector, no forward assist, A1 sights.
Then there is version that is like an M16A1, brass deflector, teardrop forward assist, A1 sights.
I have not looked at the web site for DPMS but I'll wager that the twist rate for their barrel is 1/9.
A1 barrels have a 1/12 twist rate.
They will also have a birdcage style flash hider and a bayonet lug.