What would you do?

I'm headed to PEK this Sat arriving Sun, immediately hop on a connection to HKG for 5 days, then a week in PEK.

Currently I'm booked JFK-SFO-PEK on UA 6am 757ps flight then 12.00pm 747 UD.
Looks like there is space to do a SDC, assuming fare class stays open, on the direct EWR-PEK flight, 777, which leaves at 11am something.

So, what would you do?

Leave 6am from JFK, then hope on the 747 for BF on the UD (which I've done before)

Or

Switch, leave a little later and take the 777 BF from EWR direct (I took the middle 767 BF seat a few weeks ago and it seemed short?)

I'm 6.3, athletic build, take that into consideration.
I would hugely appreciate any input.
Thanks