Best CPU for battery life

Hello,
620m vs 740qm
I have been searching around for a good laptop processor that will be good enough to play games for some years (3-4) but will not drain my battery life alot.
This is what I will be doing and how.
Games-Plugged in
AE- Most Likey Plugged in (Render plugged in)
Sony Vegas- Edit Clips plugged and unplugged (Render plugged in)
Use inetrnet and office programs-unplugged for school
My college says we will be using adobe programs (didn't list which ones though) but I will think that we will be unplugged if we use them.
I know that the 620m has higher clock speed and 2 cores but the 740qm has lower clock speed but more cores and higher cache speed. But people say that the 740 qm will drain batter life a lot faster.
I want to couple this with the mobility 5870 but will go lower if the performance on games wont go wicked far down if it helps that battery life alot.
Plan for 6gb (1333? or 1066?) of ram and 500gb hdd.
Any help is greatly appreciated, really thanks.