Two friends run duals 7s on there dirtymaxs and they look tough as hell. I personally have run a centered single 6 and 8 inch mitre cut that sit lower than the cab and give a nice look but windy days get a lil messy. (black truck so soot blends in a lil better) thats just my nickel minus three pennies.

 

id say single just bc you can run a single straight up into the bed and see how u like it for a couple weeks. if u dont like it u can plumb it for duals. if you like it then u dont have holes in your bed from support for the stacks.
that just me though

 

I have a single 6" mitre and I like it but I am getting a little sick of it and I might go to duals heres a pic.

 

heres dual 7'' aussie on an 07