M5 and M6 have higher compression and higher boost already. Because they already come maxed out, you won't get much from a tune. The X5M has lower compression to start with so possible can get more boost no?
I have one and thinking of doing a software upgrade, but what's another 75 hp when you already have 555 and the thing weighs 5500 pounds? .1 second to 60? .3 at the 1/4? Not worth destroying the warrantee over.