"while driving at 6500' plus. I consider the
performance to be amazing at this altitude and imagine that at sea
level it should be pretty surprising."

My fault, I was unclear. I meant 6500' elevation, as was implied by
the sentence that followed.
But I will respond to the 6500 RPM comment :
My experience is that they are very reliable at 6500RPMs. Certainly
more so than starting and stopping, 'carboning' up the valves and
varnishing the oil galleries.
I ran my 84 2wd 1.9 on a once a week commute for two years running 7K
RPM's for 1100 miles, stopping only for gas and one quick nap. I did
the same commute for two years with my 86 Syncro 2.1..........these
two served as daily drivers too and both went 250K+ (the 1.9 never had
a head leak, though the 2.1 did) without any breakdowns, though the
1.9 did suffer a blown coolant line and both had Vanagon Syndrome, at
first.
In short, these two ran almost 50% of their total run time, between
6500 and 7000 RPMs. I've had plenty of good luck with these motors,
having owned 11 of these vans so far. The ones I acquired early were
very reliable. The ones with more mileage had suffered poor
maintenance for too long. Good maintenance and keep my hands and the
hands of mechanics out of the engine compartment.
Don't get me wrong, I'm not a total WBX nut. I have an SVX ready to go
in one and plan on the Zetec for another....but I thought this thread
was about 2.1s modified to larger displacements.........

Gracias,
                    Miguel