Givi M11 Plate

[know your limitations]

I know this reply is two months after your original post but I'll put it anyway in case you're not sorted or if anyone in a similar position comes across this thread.
Your box won't fit to an M11 any more securely than the M5 as the important bits (the Monokey mountings) are identical.
I have the M5 on my 2002 Gen1 FZS1000 with the E55 Maxia box and it is rock steady.
Whilst between Fazers, I also had the use for a couple of months of a Bandit 1250 (you won't tell anyone, right?).
This was fitted with the equivalent Suzuki specific, metal monokey plate and I have noticed no difference between the metal and nylon plates in the security of the box mounting.

I did a video on Youtube when I installed the Monorack and plate if anyone is interested in how easy it is to do yourself. Fitting a Givi Monorack and M5 Monokey Plate to my Yamaha FZS1000 Fazer 1000
There is also a video of my Givi E55 Maxia top box too here. Givi E55 Maxia NT Top Box. First Unboxing and Fitting


Hope this helps you (or anyone else)