Well...how much room do you need/want? Do you plan on having an AMP and sub woofers? How tall are you? I personally am 6'1 and regret getting the std cab as the seat does not go far enough back.
Just because you have the 3.4 does NOT mean you can't run mini truck doublers. You would just have to find the r151f Turbo trans. Then you could have the same front bolt pattern and have the gear drive backside bolt pattern!! Of course, people sell those for $500 But, yeah. they kick butt!
Or use an adapter!
So, really you have options, but I would go for the extended cab TRD with the elocker all setup and ready to rock.