There is no disadvantage to having your parallels farther appart other then it being a bit more bulky to store. More important to the spacing on the parralles is the spacing on the spreaders. On the granberg they are adjustable. Some people see the bolt together aspect of a granberg as a weekens,s but the truth is that it is one of its biggest strengths. because the spreaders are adjustable you can move the spreaders in closer to the power head when milling narrow boards to make the mill more stable when starting a cut. then when milling a wide board the spreaders can be moved back towards the true center for better stability. I use wing nuts on my mill for the spreaders to make it easy to adjust on the fly.
imagine what I am saying in extreames. imagine if you have a streacher on each end and one in the middle of your 30" mill, a common configuration, when starting a cut on a 12" wide board you will make contact with the leading edge (the front parrallel) and the spreader closest to the power head and that is all. The only time the center spreader is in the middle of the slab as you start a cut is when you are maxing out the capcity of the mill. If you make the center spreader adjustable it can always be centered in the slab when starting a cut for better stability.
I mill with an 075 and a 42: bar so the ballance and stability is probably a bit more of an issue than with a shorter rig.
