Nice to know Helen's ride is still called Helen's ride by you all, even though we tried to rename it to save her blushes 🙂 I'll have to tell her next month.
BTW you're missing a great descent from Holt's Down into St Catherine's valley, just turn left under the underpass in Upper Swainswick, ride up onto Charmy Down, jump the gate at the top and ride over the old airfield.
As far as 50-acre goes, the official trail is fine, the thinning operations have blotted out the 'old' trails through the middle of the wood though. The wood looks devastated, but I think it'll be good for the wood long term, line of sight is much better and the official trail seems better bedded in, if anything.
Plenty to keep you going for 2 hours in a Leigh Woods/AC/50 acre loop or two.