I have done a lot of tests with different set ups from 0-4500ft.
The SLP pipe is may be a litle stonger than Speedwerx at sea level,and SW is stonger above 2500ft.@ sea level the slp is probably the best mods for the buck.
But a Jaws twin is way stronger than both single pipe at this altitude.And is even better with porting.
I did a sea level test on a otherwise stock 07 M1000 done 15min apart.
Sw increased from 7200rpm to 7550rpm and Jaws increased to 7800 with safe fuel and pumpgas.
Also this clutch kits that convert the secondary to torsen type helix (old type) work very vell, like the RKT kit.And it will work better the higer altitude because the stock clutch have a way to hard spring in the secondary that robbs hp down to the track.
Y-pipe and RKT clutch kit will work at all altitudes and is cheap.
0-4500ft: Jaws twins,40 degree rkt clutch kit and ported.The M1000 will realy goes well...no need for turbo...lol..
10000ft: RKT sec clutch kit,Hige comp head,SW pipe and porting.
At this altitude i feel RKT vill givs you what will works best.