Learned to shave with two 4/8 sized razors which is not recommended. In the meantime I have gotten several razors between 5/8 and 6/8 and prefer them which is likely why that size range is recommended. So long as what you buy is honed by a pro to be shave ready I don't think initially you would notice the difference in ease of use. If all else fails get the one you like the look of.
Bob