hi Soon,

Your temp is fine...... 77 is perfect !!!
What you need to do is get your HPS closer to the tops of your plants... Your buds will seriously increase in size.. more than double, if you can get the HPS to within 12 inches or less of your canopy. 4 feet is way to FAR..

It sounds like you have a nice system with plenty of fans and air flow...

: )
smb