The currents at peak around 79th street definitely are in the 3 knot
range + or -
There will be times when you can not sail against the current and will need motorsail to make way. You can actually sail in place..going backwards
For timing, you are close enough to the GWB that you could use that timing in eldridge.
The flood and the ebb at the GWB begin 1 hour 35 minutes after the Narrows...Eldridge has the flood at 1.8 and the ebb at 2.5. I have been sailing in those waters all summer, and believe that those are low numbers. It has felt more like 2.8 and 3.5 at peak.
For today the flood started at the narrows at 5:07 am and the ebb begins @ 10:40 am
Add an hour and a half to those times..and you should be able to plan around that.
Add about 20 minutes for each day..after today to those times....