Is a throttle body really going to get you anywhere? Every performance tuner I've spoken to, and taken both my WRX and Camaro SS to, has said they are pretty much worthless and don't really have any performance benefit.
Intake, long tube headers, no cats, H or X pipe, back to indivudual mufflers, with a dyno tune is probably the best way to go.
IMO programmers are great, but don't factor in everything. If you want to do it right, mustang dyno!