Panniers are heavy, but they do vary a lot. My Nashbar Waterproofs weigh 6 pounds 6 ounces for 2 front and two rear panniers. If you go with 4 of the front panniers the weight is 4 pounds 12 ounces. One guy here said his panniers (Arkel) and handlebar bag weighed 16 pounds empty!

I think that I would have plenty of room with four of the Nashbar front ones and may go that route next tour. With two rear and two front ones I had a lot of space in the bags even when I was over packed with way too much bulky clothing. Six pounds 6 ounces wasn't too bad and four pounds 12 ounces is even better.