Zero,
I am in exactly the same position as you but I've made the decision to jump ship!
I don't know how old you are but for me I'm hoping to have another 38years in this job and I'm sure another command will come around in that time! I would prefer to bide my time and get my command with a career airline in 7-9 years time, what's the rush?
As highlow said, the contract as a cpt you will be on will be 4/3 and for only marginally more money than the FO one (along with all of the extra responsibility and hassle!)!
Fortunately I have a base captain who I can talk to and he said that there would be no way I would get back into FR if I changed my mind mind in a couple of years! Keep in mind that the only way to get back would be by getting command in your chosen company and returning as a DEC!
So the choice is stick with the s**t you know (and the future stuff you don't know about!) or risk it somewhere else with the knowledge there's pretty much no turning back once the decision is made!
All the best!