What do you have planned for mods. Do you have any forced induction planned? If so I would trade. If not its still a toss up. Some people will say no some will say yes.
If you're planning on single turbo and AFR heads, then definately go with the 70mm. having an oversized throttle body will not hurt you performance wise. It won't help if you dont have the supporting performance adders, but with your plans, you'll have the power to use your 70mm to its fullest capabilities.