Nice grow cb! Looks like everything turned out great and your first try too. I had nothing but problems with the heat my second time around. Computer problems too so I haven't updated in a long time. Gonna harvest Saturday next week, cant wait.
If your are looking to upgrade and boost wattage everything I have seen and heard is that 600w are the most efficient at lumens per watt. I have heard that they are even better than 1000w in some instances due to the proximity between bulb and canopy you can achieve with a 600w. Check around but I think one 600w would be even better than 2 400w.
Cheers on your succesful grow man! Enjoy those fruits of your labor!