Reving up the engine. Just how damaging could it be?

[Sharky]

I've just come back from my mother's hometown where I spent my easter holidays. It is located some 400km north of where I live trough mountain, two-way roads, sometimes considerably steep, with considerable traffic, particularly a lot of lorries. This means that a lot of overtaking is mandatory which is further aggravated by the short straights and uphill direction.

When I take this road I keep the engine always above 4000rpm but during overtaking it can go up to 5500-6000rpm (saw 6200 one time though). I arrived safely so I didn't blow up the engine . However, I do wonder if it's wise to push the engine so hard during such long trips (7-8 hours). Could I be inflicting permament damage on the engine?

BTW, the car that I drive for this kind of trip is a 2003 Mazda 323 1.6L (or protege as it is called in some places).