RB
1.  If I hadn't moved, I would just meander out to the shop and look up that info.  However, I think it is stored securely in a storage locker in North Idaho, along with a whole bunch of other stuff.  For some reason, the top end figures stayed in my mind, probably because I found it interesting that the Pyrodex would provide a slightly faster MV than the real thing.  Even more amazing was the testing I did with my 8 bore rifle where it beat GOEX Ffg by 90 fps with the maximum charge I had settled on of 300 grains.  This gave me cause to think that Pyrodex was more efficient, the larger the bore of the gun.  I talked to the good folks at Hodgdon and they hadn't a clue, as no one there had tested anything that big.  Just an interresting little side factoid.
2.  See above, don't really recall, but it seems that I was getting somewhere in the neighborhood of 50-075 +/- fps increase with each additional 10 grains.
3.  Yes, I did  a whole afternoon shooting on the bench, testing various loads and lubes and patches and came up with a one hole group at 25 yards with 135 Grains Ffg, .610 round ball, OxYoke .015 dry patch lubed with Ol' Thunder and RWS musket caps.  I have found that over 150 grains in any of my big bore guns, the patch starts to suffer severe burning and for the heavy charges, I use an OxYoke 20 ga lubed cushion wad between the powder and the PRB.  Over 135 grains, it started to open up a bit, to the point where I think I was getting about a 1 1/2" group with 200 grains.  That would still be minute of elk at ranges I would shoot, but not good enough for target work.
One of these days I will get back up to my storage locker and reclaim all my stuff.  Will do some more testing when I get the chronograph back too.  Until then, I just have to rely upon a faulty memory.