given your styling desires then you probably will be fine at 50 grafts/cm
no matter the density you get, HT gives the ILLUSION of the same density as non balding areas
hair caliber per unit and diameter of shaft factor into this illusion as well
NOT just grafts/cm2
that said, trying to achieve higher densities than 40-50 grafts/cm2 will most likely yield a lower % of surviving grafts, aka wasted grafts.
so better idea to go for 2 HT each at 40 grafts/cm. this is the optimum way to prepare for HTs in general.
with "the second/third,etc. pass," it's the best chance of high grafts survival rate and an opportunity to adjust the design and areas that need more coverage.
better to go into the HT procedure knowing that you will need at least two to satisfy your cosmetic needs but might get lucky and only require one. it will also put you at ease to know that whatever isn't satisfactory to you from the first procedure, can always be adjusted in the second.
good luck