the cap of xp where the system stops working and all PC's are experts in everything?
Haven't found it yet.
Highest xp total so far in my games is around 60 xp, or 12 advancements, and the game still works.
At this stage I have noticed that the PC's that specialize have maxed out their thing - the soldier has 5 in ranged combat and all the talents they need to dakka as much as they want, the courtesan can charm and lie to their hearts contetn and so on, and they hav started branching out a bit. At the same time the more balanced jack of all trades have gottten good in several of their diciplines, like the mystic assassin who also is a face for the group? they are decent or good at all of their niches at this stage.
Some PC's have mentioned that they don't know what to spend xp on at this point, but not for lack of options - but rather it seems like getting that first skill rank in medicurgy is not as exciting as when they got their fifth in melee ...
Also, my players buy LOTS of talents, which means that their dice pools don't change that drastically, apart from that one niche .
( "a courtesan with seductive AND beautiful AND faction standing, you say? yeah ok ... maybe you want to get some skills soon? No? ok, you do you.")
For the other game where the group are in the 40xp area they mostly 'complain' that there is too much cool stuff to buy for their xp, so not really a problem