Mexico cancellation & rate query

Here is a link to an image of a cover in my collection, mailed from my
home town of Silver City, New Mexico to Mexico City in 1895:
http://www.ingraham.ca/bob/silver_city_cvr.jpg

My understanding is that the letter rate from the U.S. to Mexico was
lowered in 1887 to two cents per ounce from the previous five cents
per 1/2 ounce. I'm wondering whether the 5-cents postage on this cover
was an overpayment because the Silver City postmaster was eight years
behind the times, or whether the rate for an overweight letter might
have been five cents per ounce. Or, alternatively, the rate might have
gone up in the intervening years. Any information would be
appreciated.
Thanks,

Bob

A P.S. to my previous post:

My apologies for that misleading thread title: I did have a question
about one of the backstamps, but I figured it out.

Bob

A further question about the aforementioned cover: One of the
backstamps is that of El Paso del Norte (present-day Juarez). Was it
common practice to backstamp covers when they crossed international
boundaries, in this case from the United States to Mexico? It's not a
receiving postmark, because the destination was Mexico City, and there
is a "MEXICO D.F." backstamp; "Mexico Federal District" is a Mexican
term for Mexico City.

Bob