Damian wrote:
"i dont care about speed. its 300mb/s and its enough"
That's what they all say....
The internal PCI-e based SSD in the new iMacs will run 3x to 4x faster than a plugged-in booter (and I'm an advocate of "external booters" in this forum).
The difference will be quite noticeable.
But something more important:
I'm not sure if your best approach is to use a single external booter on both the new iMac and the MacBook.
I just believe it's better to set up each to "be its own Mac", so to speak.
Of course you want to share stuff between them, such as data.
Easily done with your portable drive.
But for the OS, let each Mac "be its own booter".
Consider:
If something goes wrong with your thunderbolt drive, you've lost it all.
But with each Mac running independently (with backups, of course), there's a much greater probability that your DATA will "live on" ...