I went to the range today and and I shot the JS FFFG in the TC hawken today. Here are my findings shot at 50 yrds with 460 Great Plains conicals (total of 20 rounds fired):
75gr- Not a very good group... measured in 1/2 feet (3 shots).
80 gr- Great sub 3" grouping but shooting 6 inches lower then my Pyrodex FFG and I have no room to raise the peep up any further. Will play with this after hunting season.
85 gr- the height came up but it was a 5 inch group. Cheek starting to get sore so I may be at fault on some of the shots (4 shots).
90 gr- all over the paper but I onlytook 3 shots

At 100 yrds I was missing the paper on all of the loads but I am not sure if I was high orlow. I only took a couple of shots with the 80 and 90 gr loads.

Clean up:
While there was less fouling in coming out of the barrel I did notice that the barrel was tighter with the patch and cleaning jag going down the barrel as compared to the Pyrodex. Note that I did not clean up between rounds as it is below freezing out side (minus 5 C) but loading became a little harder after the 1st 2-3 shots and then stayed constant. Not cleaning may have been a factor on the groupings.

Conclussion:
The verdict is out as I will need a bit more testing but I will be shooting the Pyrodex till after hunting season! Maybe longer.

My 2 cents
Eric