Lamont.
Gatti was never legit at 140.
If you can box even a little he would struggle.
At 135 he was close to elite IMO with that power.
Gatti's best weight was 130, he was rather poor at 135 with his 3 straight losses in 1998.
Peterson probably takes a decision here.
lamont in a great fight
he's the more consistent boxer
has the better defense and chin
and he's bigger
gatti has better handspeed with his combinations
faster feet
a better workrate
and obviously he was a fight changing puncher, even at 140
peterson via stoppage on cuts or swelling, especially if they went past the 10 round gatti special.