Does this look weird? +8cm femur mockup

I think the saving grace here is you seem to naturally have a quad dominant build, so making your thighs even LARGER to really smooth out the new length will be a cakewalk.

PS given a 5'5.5 starting point, having a long looking femur should be the least of your concerns.

Got it. Might be hard to tell without another mockup but do you think shaving a half inch off the lengthening would look significantly more natural?

I was about your same starting height.  I did 7cm and am honestly glad I stopped at there.  I think 8 almost would've slightly put me over for proportions, but I'm happy I did what I did.