4.6 V Valve Intake

The stock PI intake is a great intake for most people- has nice lower end with plenty of upper end all while being lightweight.

For gains on the upper end (5k rpm+) without losses down low look at the bullet intake or the trick flow street burner (not the track heat version!)

If you are looking for something more serious then find a good mustang tuner / mustang shop and see what would be the best combo to complement a serious turbo setup-
If you are spinning 7k rpm+, serious drag racing, etc then people had varying degrees of success (potentially with low end rpm losses) with the following:
HPS Hard baller Intake
Foxlake P51 Intake
Professional Production Typhoon Intake
Trickflow Trackheat Intake
Edelbrock Vic.Jr Intake w/Custom Elbow
Logans Sheet Metal Intake
BBK DSI Intake
Reichard Racing Intake