I have got both my Shadow and SP-01 to make weight for IDPA. The SP-01 only required lighter grips. Google Dennis Marshal. Their grips are made in Hungry and weigh next to nothing. I paid $45.US for my set.
The Shadow was a little more challenging but I got there by:
Replacing the grips with Dennis Marshal grips
Replacing the mainspring with a 15# spring (the spring weighs less)
Replacing the factory mag brake part with a an old style mag brake made for the CZ75B, then narrowing it to reduce it's weight further. One of our shooters windowed his mags to reduce the weight of his Shadow. I believe he has a tenth of an ounce to go to get to the magic 39 oz. He also went to Dennis Marshal grips.
The "Tactical" should make weight with just a change in grips.
Personally I think the Shadow is the better purchase as you get a pretty good trigger pull out of the box, great sights for playing the games and a slightly different frame. The Shadow is cut more under the trigger guard and at the base of the beavertail.
The SP-01 frame was made in 2006 while the Shadow frame is stamped 2008 which may account for the difference in frames noted above. The weight difference between the two maybe the frame difference as well as the SP-01 has a firing pin block and the slide and frame have been cut out for the firing pin parts.
Take Care
Bob