Maximum skill level by TL

[cmdicely]

Originally Posted by cosmicfish

But then the numbers are just decorative... I am looking for a more applicable, less hand-wavy (or at least more consistent) rule.

Its probably not possible to do anything that works well in a general sense for all TL skills. For specific skills, well, you need to detailed handling of the skills to address them. For lots of skills, the relevant GURPS "Tech" (Low/High/Ultra/Bio) books discuss what the skill can and can't do at various tech levels and with/without particular equipment.