Livre d'Or

I think 20-30% is more likely in science in the UK too. And a PhD (even in science/maths) has almost zero value outside academia unless it is VERY specifically work related. There are only so many highly paid city number crunching jobs to go for.
Seriously, getting my Ph.D. in my early 40s had the effect of wiping 16 years worth of senior management experience off my CV which took some efforts to overcome.
I have no regrets though, I always dreamed of doing a Ph.D. and "they" can't take that away from you.