Touring - Panniers

I'm looking for some advice on panniers. I need panniers for commuting and running errands. I have no set plans, but am looking for some 4/5 day light touring trips (everything but a tent). I sometimes get groceries with the panniers and am intrigued in having one that converts to a bag for shorter and lighter trips for city rides.

What do I get out of spending over $100 for Arkel vs. the cheaper ortlieb and MEC. I like this bag http://www.mec.ca/Products/product_listing.jsp;jsessionid=GH7GTtvvK16hJhhQGx306g36jgg6TWpKnx20YJ1JdL4TvHvQVVy8!734425161?FOLDER %3C%3Efolder_id=2534374302693317&bmUID=1174928262052
since it converts to a day pack, but would buying two of these be substantial for light touring, or do I need at least 40L?

Thanks for any help.

I'm looking for some advice on panniers. I need panniers for commuting and running errands. I have no set plans, but am looking for some 4/5 day light touring trips (everything but a tent). I sometimes get groceries with the panniers and am intrigued in having one that converts to a bag for shorter and lighter trips for city rides.

What do I get out of spending over $100 for Arkel vs. the cheaper ortlieb and MEC. I like this bag http://www.mec.ca/Products/product_listing.jsp;jsessionid=GH7GTtvvK16hJhhQGx306g36jgg6TWpKnx20YJ1JdL4TvHvQVVy8!734425161?FOLDER %3C%3Efolder_id=2534374302693317&bmUID=1174928262052 (http://www.mec.ca/Products/product_listing.jsp;jsessionid=GH7GTtvvK16hJhhQGx306g36jgg6TWpKnx20YJ1JdL4TvHvQVVy8%21734425161?FOLD ER%3C%3Efolder_id=2534374302693317&bmUID=1174928262052)
since it converts to a day pack, but would buying two of these be substantial for light touring, or do I need at least 40L?

Thanks for any help.

Not a touring expert(going on my first real tour in a week,actually) but own 4 Arkel panniers. What you get when you pay the big $$ for Arkels is superb quality, lifetime guarantee, great customer service (to the point of sending replacement parts to Israel for free), extremely well thought-out design, durability and style.
They are very expensive, and the shipping to Israel doubles the price(almost) and still, i wouldn't even consider other bags for my next purchase. I've been commuting for about a year and a half now, every day, and apart for a small tear which is my fault, the bag(s) are in perfect shape.

What i don't like about these Mecs(first time i ever see them) is that they are made in Vietnam, and as for the convertible daypack - you have to take off the hooks when you want to use it as a backpack. Seems like an unnecessary hassle, and probably doesn't last long either. And it probably has less features than the Arkel Bug, or Commuter, Briefcase or GT18BP. Not that these features alone are good enough reasons to splurge for the Arkels.

I learned the hard way, that being cheap results in having to pay twice as much. So i just go for the best (within reasonable bounds) i can put my hands on. Especially with things like bike equip. that has to withstand enormous stress and be very user friendly in order to keep you happy.

G'Luck.

Edit : You asked what you get when you buy the Arkels. That's what i addressed in my reply. By no means did i imply that Arkel are the only decent bags out there and that they're the only ones you should consider or that they're the only ones that get the job done.
You probably could, and people do, get by just as great with another brand.

Those look a little small for you. If you are doing lite touring and commuting, you don't need the super bags like Arkel.

You could get the small ones now, and the big ones later. That's what i did.

There's A LOT of threads on panniers here. Recommend you do a search for "Panniers" in subject line