There is a rule of thumb that within a group of people, the number of people who carry the most weight is roughly the square root of the group size. For a party of 4, then about 2 will do the lion's share of the work. For a party of 6, that comes out to 2.45 people, which is not that much different, but a little. Once the Bag of Holding became available in the BG series, there was suddenly a lot less need for six party members. I much preferred adventuring with and fighting alongside uncontrolled NPC's such as Narlen Darkwalk, Gorpel Hind, Drizzt, etc. Six of those would be awesome!
