i sometimes have similar issues to this, but i'm lucky enough that most of my retro stuff hasn't cost me too much so i don't feel i need to justify selling 1 bike to get another, i just save more or wait for new projects to come along, my O for example, the frame was cheap as nuts and it was built out of spares except for the wheels which came from my oldest clockwork that weren't correct for that bike but then lucky enough the following week the right wheels components showed their face for the clockwork.
also i agree with scant, i have riders and garage queens, and i hate that really, they should be ridden otherwise it's a waste. but i view the bikes i have that are garage queens more as part of a collection, museum pieces i suppose. they are functional and working but only used occaisionally on dry day special occasions like showing it off at events like when i brought my clockwork to ssmm to show it.
the modern bikes get ridden most, the 07 clockwork and st4 then the cyclocross bike, the O gets used for work, the c16r for nice days the 93 clockwork is the full on queen and the newly added kona is the rider retro coz it's not immaculate!

and i haven't used the d2 much coz i'm bored of road at the mo but i do happily ride it usually.
in your situation assuming it is a 1 in 1 out style i would keep the 96 p7 out of your retro machines because it is the older and therefore more retro model and even though you have a clockwork i feel the p7 you have is more iconic than your particular clockwork. i really agree you should not sell the 5, that is a very good bike, possibly the most perfect (imo

) allround full susser available today, simple and reliable.
i do conceed that the modern bikes ride nicer hence riding mine more myself, but i'd hate to part with any of my bikes, i'm at the point where all my bikes that are modern are relatively limited so i wouldn't want to sell them (frames specifically) either!
it is a massive dilemma if you have to decide, good luck deciding, i don't envy you!
