Is there a way to tell G I accept the offer but I will start next year 2nd quarter.
Because that is unreasonable way of doing things
$100k seems like a lot, and it is in real terms. I find that people can some times get tripped up by the total amounts though. In my experience it's usually (but not always) better to keep momentum and go to the better company sooner.
It might actually be worth explaining the situation, and asking to start team match after the new year. I don’t know their policy, but they might be willing to compensate you with a higher on hire bonus to get you to quit.