if I remember correctly even the old bgs were a maximum of 4, but I could be wrong. Honestly with a group of 4 there is a lot more strategy and I personally like it. Six would be too much, they should increase the difficulty of the mobs and should increase the mobs to face.
The origional Baldur's Gate games both had 6 man parties as the default party size when you was done recruiting companions, as did the Icewind Dale games that where built on the same engine. If they where all based around a 4 man party then this wouldn't be such a big deal to all of us who loved the originals.