The individual 5000 cells are better than the 4000 cells that the 8000 pack is made up of, on an individual basis. That is, comparing them cell to cell, but in the 8000 pack, the 4K cells are wired up in parallel. I think that the 8K packs are great. I've never had any problems with them.

If cost is a concern, you might also want to check out the truerc packs. The aren't the latest and greatest, but the 8000s are great for the price. For little more than the cost of one maxamps pack, you could get two truerc packs.