I've been waffling between standard red and Olde Enysford for a few years, mainly in Fg grain. Here is what I notice.
Grain size/shape appears the same for both
Velocity is slightly higher with OE with equal volumes; 5%-10% faster, nothing crazy. 10 extra grains of powder does the same thing.
Weight by volume is almost identical
Shotgun patterns are similar, those in the BPCR community seem to prefer OE
And the big one everyone keeps asking is fouling. If anything, OE is worse than Red. There's so many factors to this that it is hard to say with certainty, but it sure seems to me that OE fouling is much more dry and solid. It isn't that there is more of it, but it takes just a little more to clean out. By contrast, is seems to me that standard Red fouling remains soft and powdery, at least for a short while.
I've also shot a few pounds of FFg of both types and found the exact same observations. There really isn't a world of difference between them for muzzleloaders, unless maybe you were into really long range shooting. Being as Olde Eynsford is no longer in stock anywhere, in any granulation, and may possibly never be made again, there's not much choice.
BTW, Powder Inc. has standard Red Fg in stock. I just ordered 25 pounds, and it is sad to think that may be the last Goex I ever buy.