I have never tried this in GURPs, but I have played other games where there were large discrepancies in the starting powers of the characters. I have tried mixed old World of Darkness games with different species and different versions of DnD with widely separate starting powers (in fact, this almost happens naturally in later versions of DnD if you have skilled optimizers next to non-optimizers) and a few others.
Generally, it has been my experience that widely different power levels do not work well together. Someone will end up feeling overshadowed or someone will end up carrying most of the load, and it makes the campaign very hard to design for from the GM's perspective.
I know of two exceptions where it works quite well though.
For a new player, especially if they are a guest.
If you have an existing campaign going and you are bringing in a new player, especially someone who is new not just to the campaign but to roleplaying in general, then it can make sense to make them somewhat more powerful than the others. This makes it easier for them to have a chance to shine and it makes things more "fault tolerant" since the character has enough power to survive novice player mistakes.
I'm not actually recommending this as it can cause problems down the road as that player becomes more comfortable with role playing but still has the strongest character. But it can help introduce someone to roleplaying in a positive way, especially if that person is a guest that won't be able to play through the whole campaign or if it is meant to be a short campaign anyway. I've been on the receiving end of this when I was much younger and a new player and it was quite pleasant for me.
If someone wants to play a weaker character for narrative reasons.
I like gishy characters (fighter/mages). I will take a gishy character even if I know full well that it is suboptimal, as long as its not so suboptimal that I expect it to cause real problems in the power level.
In World of Darkness, the character types are not all made equal. Mages for instance tend to be more powerful than vampires and everything is more powerful than ghouls. But some people will knowingly take a weaker character type because they like it better. As long as the power discrepancy isn't so big that it will cause problems and as long as the player realizes what they are doing, this can work very well and keep everyone happy.
In general, I really think the power levels should be close to equal. There are some exceptions, but those exceptions work best when the differences are small rather than huge and when everyone at the table understands what is being done and agrees to it.
I haven't played GURPS, but that looks like a pretty big power spread and I'm not sure how well it would work.