Steady on, mad_for_it, it's only a hypothetical question after all. In answer to it - I think the current "chance" system works best, considering the *average* lifespan is over 70 years. Having a guaranteed 48 years would lower the average by more than 20 years. OK so there's a chance that those of us who aren't 48 yet could get run over by a bus tomorrow and lose out on our remaining 8 years, but statistically this is less likely than surviving beyond 48.
have you been watching Logans Run by any chance (or was that 30) and can i ask how you arrived at 48 as a fiugre for the lifespan? and chance every time! How depressing would your last year be knowing your ticket was up shortly better to live life to the full "carpe diem" and all that eh?