In reality any performance gains will be mostly placebo, affect less that 5HP. SO if the purpose is truly for power, leave it stock, and save for a bigger bike. The difference between a Shadow 750 and a VTX1300, is much bigger on paper than it is in the saddle. Bigger bike being much easier to ride at speed and for distance. If your main purpose is aesthetics, visual and aural, go for it.
93 VT1100C Harley Killer (1150cc), VH Exhaust, 2mm sleeved and bored, Modified Heads and Valves, Adjustable Timing, Touring Seat, Baby Apes, Metzlers