Best Performance Cam ?

I have a GT-40 Ford Racing Crate Motor with B-303 cam in my 93 GT Mustang.
I'm thinking of putting a more aggresive cam in at some time.
My car is street legal, emissions here in Massachusetts won't be an issue after this year. I mainly use my car for drag racing, not a daily driver.
What cam would give me the most horsepower for drag racing with the motor that I have? Or is the set up that I have now just about all I can get out of it.
I have seen that there is a x303 and a z303 from Ford Racing.
Would these cams work with my motor?
What type of work and changes would the cam swap involve?
I have never done one.
Thanks for all the help.

I thought the b-303 cam was more aggresive than the e-303.
I won't be adding forced induction.
My set up is
1993 GT Mustang / Ford Racing GT-40 Crate Motor B-303 Cam / 24 lb. Injectors / Stock Ignition / MSD EFI Blaster Coil / Edelbrock 5.0 Upper and Lower Intake with BBK Phelonic Spacer / Professional Products 70mm Throttle Body / C&L C.A.I. w/76mm MAF / Stock Air Box w/K&N Panel Filter / Holley Adjustable Fuel Pressure Regulator / Electric Fan / BBK Underdrive Pulley's / A.C. Removed / BBK Short Headers / Flowmaster Exhaust / Tremec T-5Z / B&M Short Throw Shifter / Alum. Driveshaft / 3.73 Gears / Eaton H.D. Posi / Moser 31 Spline Axles/ Subframe Connectors / Line Lock / Driveshaft Loop / B&M Short Throw Shifter / Racing Upper and Lower Control Arms / Lakewood Adjustable Drag Shocks/ Holley 190 lph Fuel Pump /