If I was you I would go Loka and medium ICU to be safe - but if it were me personally I would get a medium or small shallow ICU - not the PRO size.
I am speaking with out the flashes though... And if you are packing flashes I would grab a Micro ICU for those and stack the ICU's.
Loka is my personal favorite bag to ride in and I use it for most missions. The Tilopa is still ride friendly as it is only as big what is inside. It compresses to what ever you need it too.
We did design the Loka to be a more ride friendly photography backpack. Loka would be more enjoyable when actually snowboarding/skiing with the load you said.
We did update the site recently with a lot of lens combo's in ICU's. If you have not seen it --
http://fstopgear.com/en/icu-shallow