Well, the difference between 1e-5000 and 1e-5100 is pretty small. For most intents and purposes, there is no difference

Heh ... I thought this was about "mathematical equality", but suddenly it's now also about "intents and purposes".
For double precision NVs I could have chosen much larger values of (say) 1e-324 and 1e-325 ... but you're probably not going to be swayed by that, anyway ;-)

By my calculations, the latter is 659669 orders of magnitude bigger than the former

Yep, I get the same:

C:\>perl -MMath::MPFR -le "$x=Math::MPFR->new(6 ** 6); print 6 ** $x;
2.6591197721532269e36305

C:\>perl -MMath::MPFR -le "$x=Math::MPFR->new(7 ** 7); print 7 ** $x;
3.7598235267837884e695974
[download]

Cheers,
Rob