"Vnav logic regarding the accel altitude after takeoff in the NG"
No such thing in our 800's with FMC U10.6. There is no entry prompt like that on the Take-Off Ref or CLB pages, so after departure if you hit/call for VNAV the A/P or F/D will command an acceleration to 250 kts (if you have a speed restriction at 3L on the CLB page, something like 250/10000' that is...)
Our company procedures are to call for/engage VNAV when Flaps are UP, reason being is that VNAV will accelerate to 250 kts regardless of Flap position. I believe that new FMC updates are already out that allow VNAV to be engaged before T/O on the ground, but I haven't seen 'em yet.
(you can mess around with the old FMC's to be able to engage VNAV right after departure, but it's a drag...I wouldn't mess with it)
Big Boeing s are more sophisticated....