I was the same as you, I thought 6cm is nothing. But trust me when I tell that 6cm is a lot. More than enough. And if you still are unhappy you can still go for the second one.
I trust you two my friends (123 and upland).
Last month i was very greedy for 9.5 cm on femur
Then many diaries realized me not over beyond 8 cm for greater recovey.
But 8 cm on femur is not good for femur proportion when compare with own tibia
Andrew schizzle not have a good propotion femur/tibia .
Blackbear from old forum also have long femur even he also lengthend his tibia when he did deadlift in video it was very obvious that he has very long femurs
then i am going to realistic amount femur not over than 6 cm (5-6 is enough) and then plan did for tibia 4.5-5 cm
In case i will consult with dr paley about which methods (maybe now not only for precice )then my aiming goal is 177.5+5.5+4.5
.i think it greater recovry than 8 cm only femur(precice) .and femur and tibia still in good function
My plan 1st day do femur
Then 21th do tibia
It use only 70 days from start to complete 10 cm ,shorter time and stronger bone(less lengthend) .
I see many evidence from dr dong hoon lee youtube
He has many patients that did both femur and tibia and could run with12 months ,loads of video there.
This is all my opinion