Dusty old post...
I realize that this post is old as dirt, BUT no one answered it here... until now -
What the OP is asking is 100% true... spot on. Installing a HL cam on a Q2XL... using the MQ1 cam in 80% let off (SL-letter-[R]or[L]HL) will work just fine.
To maintain draw weight and tune when changing from 70% to 80%, a longer string and a slightly shorter cable will be needed. The HL cam has a large lobe to contend with. Matching the specs from the MQ1, (which came in both 70 and 80% let offs), keeping the limb deflection as Mathews intended requires that one adds 2.5 inches to the string. Likewise to maintain the tune, reducing the cable by 1/8 inch is also necessary.
I've done this very swap for a buddy with shoulder problems who shoots the standard Q2. His bow paper tuned perfect bullet holes in just three shots. Very minor rest adjustments and this bow breaks nocks. Not to mention making it much nicer for him to hold at full draw. :thumbs_up
