...This is too much work for a forum post. I'm coming back to this later.
I think we probably get the gist enough to agree the general thrust. No need to make your brain explode ! Or am I just projecting?
You're right. I'm not going back and changing everything. The math is a little wrong though for the given situation. People get the point. I think combat illustrates it best, as does a repeatable roll: n*i*(1-(b^n))=z Let us suppose there is a party of 4 and a party of 8. Let us also suppose there is only one side on the die which gives us success. Therefore, b=0.95, i=multiplier, n=4or8. For a party of 4, overall combat effectiveness, z=0.742i For a party of 8, overall combat effectiveness, z=2.693i So a party of 8 is NOT merely two times stronger than a party of 4, but IS ACTUALLY 3.629 TIMES STRONGER THAN A PARTY OF 4.
That is unsurprising and surprising at once. Though, of course it depends on whose hands its in. Imagine 8 fireball sorcerers, 32 fireballs on the first turn (muahaha).
Though, without the cheese, the amount of extra times you can cast haste and such... it just turns otherwise "merely" strong tricks into cheese. There's not much difference between a 8 person party and giving yourself infinite hp. You can, but most people won't find it fun
I'd still advocate for a hard mode with buffed enemies and 6 party members, though! More tactics, appropriate opposition.