I've copied the characteristic advances (e.g WS +5 costs 100 for a rogue trader) in an excel sheet and looked at the differences per class. And came to the disturbing conclusion that if e.g. a Rogue trader were to buy EVERYTHING to a +20 it would cost: 24.300 XP while if an astropath would do the same it'll cost her 27.450 XP thats 3.150 XP MORE!!
Now you could argue that perhapds the skills or talents are cheaper or have access to 'better' but although its pretty hard to compare, I don't really see any difference between the two, save the fact that I'm inclined to say that the Rogue Trader got the better of those too. (but that's arguable).
My question is: why is there a difference AT ALL? I understand that +5WS for a RT is cheaper then a +5WS for an astropath and vice versa for WP, not arguing about that, but the total costs to advance IMO should be the same all over. Actually I would expect event the totals per step (simple, intermediate, etc) should be the same.
Now before I go messing with this I first would like to know if I'm overlooking something vitally important that explains this.
Here a short list of the total costs to set each stat to +20:
Rogue Trader 24.300
EDIT: after looking at it better I've seen some patterns which can be generalized over all the characteristics. If you do that you will come to the following conclusion
Simple 100/250/500 2/5/2
Intermediate 250/500/750 2/5/2
Trained 500/750/1000 3/3/3/3
Expert 750/1000/2500 3/3/3/3
E.g. There are 9 simple (+5) advancedments which either cost 100, 250 or 500 XP. It turns out that the most common is 2 advancements cost 100XP, 5 advancements cost 250XP and again 2 advancements cost 500 XP. You can use this method to adjust all the XP costs for all careers. If someone is interested I can post a link to an xls with these changes.