Which skills are worh raising really high?

[maximara]

From the GURPSwiki:

Extremely High Skill Not Needed

At first glance a mythological hero able to skewer foes while fighting from his back, with the wrong hand, while dealing with poor lighting, and injuries would seem to require a 40+ skill but there is a saner (and cheaper) way to do this.

The warrior should be a master (level 20) in their base weapon skill, have the Blind Fighting skill (which negates darkness penalties), High Pain Threshold, and the techniques Ground Fighting, Hit Location and Off-Hand Training (removing penalties for position, hit location and off-handedness respectively).

"The essential point here is that highly-skilled character concepts can be realized in GURPS through the artful use of reasonable skill levels that do not break the system." - Compendium I p. 114-115

Sending skills or attributes into orbit IMHO ignores all the other ways that can produce similar effects. The fan made GURPS Mummy did this and the wiki provides ways to not do that...and the original was using attribute 40+ (yes that is forty plus) to do its thing.