Hell's Gate & the East River
I made this trip last November on my Pacific Seacraft Mariah 31, and it was a blast. Like you, I obsessed over this portion of the trip for weeks; the truth is that if you time it just as you describe, you'll find yourself flying past manhattan in no time, and having a lot of fun in the process.
My only word of caution would be to watch out for sudden strange changes in current while riding down the east river in such a strong tide. Once your through the scary hells gate portion of the trip, it's easy to get complacent and think the worst is behind you, but I had one or two surprise course corrections due to turbulence. Nothing to worry about, just stay on your toes until you are through the Manhattan bridge, where things start to widen a bit.
Leaving at 8 AM from Stamford CT, I made it into Chelsea Piers on the Hudson River side of manhattan around 3:40 pm. A fair amount of that time was spent fighting the same currents that rocketed me down the east side of the island as I travelled north on the Hudson.
If you find yourself tempted to overnight at Chelsea Piers, drop by for a sundowner. I'm on Pier 70.