Tony Williams just pointed out my mistake.
I'm so used to dealing with SMPS inductors I forgot we were talking about a solenoid.
In a SMPS inductor (or transformer) some external circuit is used to limit the current - pulse width, peak current control etc, and in order to minimise losses, Rdc is very small. In which case V = LdI/dt is the "right" equation to use (as I*R is very small)
but a solenoid or relay isnt (generally) used that way - Rdc sets the current, and is most assuredly not "very small", and of course I*R = Vcc which is not "very small"
in which case its more about L/R time constants. I = Vcc/R, so when you switch the solenoid off, the voltage across the internal inductance rises to Vcc (because of I*R) + Vclamp.
So the difference between 42+5 and 42+0.7 is bugger all, and the difference in decay time is, likewise, bugger all - well not bugger all, but certainly not 7x.
Oops.
Cheers Terry