Ideally, flex-wise the Stiff high-back Targas are a better match for the stiff T.Rice than the softer high-back Bosses. However, I personally would slap the 390's on there more so for future swappability. Although the Targas have an adjustable flex ankle strap, the stiff high backs will pretty much leave it as an option for only stiffer boards.
Basically put, if you think that you are going to be using these bindings for multiple boards in the future, the mid-flex Bosses are the ideal choice. If you are going to keep these bindings attached to this board or other stiff boards, the Targas are a better match.
Both have the cant system and super comfy straps so you're all set in that department.
Although I always recommend matching the flex of the binding and boots to the board to people, I myself don't do that. It's just a personal preference of mine. I use mid to mid-stiff bindings on any type of board with mid-soft to mid flex boots. It's just what I find to be most comfortable for me.