You also have the option to pc from your freedom to the slate and pc the slate to a csp since you already have the freedom. Think that will be much easier than trying to pc both cards.
Are you not eligible for a CSP SUB? Is there a reason to not apply for a CSP.?
I would make the shift as move $1k or $2k limit from the Freedom to the Slate, then PC the Slate to CSP.
I would apply for the CSP to get the signup bonus, and PC the Slate to Freedom Unlimited. Then you would be earning URs on three cards.