Got to love a plan that comes together.
Spray with an everything killer. Wait till it dies then in 2 weeks later plant grass that you want.
I was saying spot treat it and kill the bentgrass you want gone then plant the seed. You do not have to kill everything. But if you like the Tenacity idea try it. I do not like bent frass. It does not grow tall to get a plush grass but to each his own.