Give your customers a choice and let them decide price vs speed as long as you feel the 'value' equation works and isn't "are you kidding me" at the fast end as that can drag down your whole brand.
Then on the longer delivery, be very very very clear upfront pre-purchase both the time window and why (your value to them) and perhaps a few alternatives that reduces time (even if few days it gives customers choice and shows your 8-10 value). Also OVER communicate with simple clear email that show where their order is in the process and time left.. otherwise you'll be hit with lots of customer calls and potential cancelations.
Set your value, add choice that can also show your value, over communicate preorder and after order.