I'd rather trade Gortat to OKC for the 12th pick + Perkins because I'm afraid OKC is going to take Dieng and I want us to get him. The downside is that it costs more... I think Perkins is signed for two more years. Or maybe trade him to Portland for the 10th pick...
Those moves aren't mutually exclusive though.
The Suns can take on Marion and the Mavs pick and not necessarily have to send back another player. Theoretically the Suns could send back something like 2 second rounders for Marion and the pick. Or perhaps the Suns send back a cheap body like Garrett or Tucker to help the Mavs fill out their roster. I'd be thrilled with that.
Then with Gortat, the Suns need to play OKC and Portland gained ech other. Perkins is awful and has 2 years left on his deal. So if the Thinder want Gortat, an athletic big who can run with Durant/Westbrook, ask for Lamb and the #12.
Portland wants a quality Center to play inside and compliment Adriges midge game, Gortat is an ideal fit. From Portland the Suns wouldn't need to take back a Perk like contract JD the pick is slightly better. Offer Gortat for the #10 and the Blazers would have to send young cheap filler to make it work (ie Freeland, Jeffries and Barton).
In fact you can do them as related deals. Do the Portland deal first for instance, and then you send one of the young guys (or one of the Suns young low/no upside guys) to Dallas as part of receiving their pick and Marion.
I'd love the Suns to have picks 5, 10, 13, 30 and Shawn Marion, that'd be great even in a weak draft. The Suns need to be aquiring assets and that's what those deals would do. Maybe you then combine picks to move up, flip them for other assets or whatever.