my version at 2 weeks is as close to fullers esb as i have ever had and i usually drink most of it around 52 degrees. it dries out with age though but for the first month, its perfect. i am not overly careful about getting some particulates into the keg either and i think this somewhat simulates sitting on the lees that a real ale does. it makes for a bit of a cloudy pour for a few pints but adds character. in my experience, fullers esb is a delicate balance of malt and ekg character with a very smooth mouth feel. the hops are present in the aroma but not dominate. same with the flavor. i get ekg in the front with a mellow bitterness in the back tamed somewhat by a subtle caramel note.
have you ever tried the partigyle?
how much gypsum do you use in how much water?