Quick advice needed on iron shafts

I intend to buy a used Mizuno Mx-200 golf set over eBay.

Need advice on the flex of the shaft. I know the best is to try to custom-fit but I am just seeking a quick opinion.

I am currently using NSPRO 950 Stiff. Ball flight is ok but I tend to over-draw it all the time. it's not to the extend of hooking. (it could be the indian not the arrow) I like the lightweight of this shaft and the overal feel of it although it did occur to me in my mind that I may get more distance with the regular. Hit my 7I pure to 150m.

Considering the True Temper Dynalite Gold XP R300.

Anyone with 2-cents worth of comments?