Tony - I'm suggesting 450 as a minimum only with regard to the new Ilchester to Avalon section. This number is based on two recent runs there and takes into consideration shallow, sharp rocks we encountered in the mile below Ilchester in the wake of the dam removal. Mark Brenneman (present on the first occasion) and Lisa Laden (present on the first and the second) would place the minimum at 475, in fact. Our runs were at 475 and 493, respectively.
I've had enjoyable runs on the main section, Old Frederick Rd to Ilchester, down to 300. I'm sure you could get down it at the lower level you mentioned, 244, but portions before the bigger rapids that were already bumpy/scrapy at 300 would be even more so. Personally, I'd take a pass if it were below 300.
From: Tony Allred
P.S. Here are my feet/cfs correlations for the Hollofield Gauge on the Patapsco (2.0' Hollofield was the traditional zero):
2.0' = 244 cfs
2.8' = 680 cfs
3.0' = 828 cfs
3.5' = ~1,200 cfs