Zip-Off Pants

For a one-week walk I would certainly not be going out and buying new pants. I'd use what you're used to - the weight difference is surely minimal in the overall scheme of things.
OTOH if you have non-zip-off pants and think you'd be happy in them, then perhaps take those.....so long as you don't mind walking in longs if you get the odd hot day.

I think you will find the convertible pants a good choice.

Although I have never done a Camino, I think that what you gain in versatility from the convertible pants more than offsets the small weight penalty.

For example, the bottom portion of the pant is more prone to getting wet, soiled or torn so it's a benefit being able to unzip them to dry/wash/repair without having to change into another pair of pants or shorts. Whilst this may never occur, it is nice to know that you have the option.

I find that earlier generations of convertible pants were somewhat uncomfortable (and noticeably heavier) due to their bulkier zips but the current convertible pants are almost indistinguishable from normal pants in comfort.

My zip-offs are shower proof. I carry a pair of lightweight breathable waterproof trousers which are lighter than gaiters and also provide an easily removeable windshield if it is cold in the morning. As said above if the zip-offs do get muddy then it is easy to just rinse off the bottom section. It just depends how crucial the extra bit of weight loss is to you IMHO.
Buen Camino

I also have a raincoat/poncho which is very similar to the Altus/Ferrino. It comes down to my calves so I was intending like you, to wear gaiters to protect against rain/mud. I didn't want to take rain pants due to the weight and having to put on an extra layer over my pant, especially as I perspire a lot.

I'm a bit of a gear nut so I may have a solution for you that will do away with the gaiters although it will require some extra expense and effort!

I went to a clothing alteration place and had them cut the bottom half off an old pair of Columbia rain pants and sew on the matching zip from a (coincidentally) Columbia convertible pant. In inclement weather, I zip on the rain pant bottoms and am protected from the knees down. The rain pant has side zips and Velcro fasteners so I can put them on over the boot and they provide a good fit around the boot top. I find they're also more comfortable than calf gaiters as they are part of the pant leg and don't cinch around the top of the calf.

I did have to buy two pairs of the convertible pant and sacrifice the bottom legs of one pair, but for me it was worth it. The second pair is my change of clothes so it is not wasted and either pair of bottom legs, rain or normal, are interchangeable between the uppers.

So far the downsides I've noticed are that the rain bottoms have a slightly clammy feeling and they look a bit strange as the tops are sand coloured and the rain bottoms are navy blue :shock: When wearing the raincoat, it just looks like I'm wearing full length rain pants.

Clearly this is not for everyone but it works for me as I had the unused rain pant available and I only needed rain/mud protection from the knees down.

Lowe Alpine has gaiter pants:

http://www.sierratradingpost.com/lowe-a ... rFamily=01

There is not a good size selection here, but other places on the web may have them.