I have been debating about this very issue as I contemplate my third child entering Kindergarten in the fall. He's 4, and we've been using Saxon K this year so he feels included in school. It's really very gentle, and seems to be right on level with his abilities. However, I hesitate to go full steam ahead with Saxon 1 in the fall. He's got a very strong and (ahem) stubborn personality; I'd like to avoid as many battles as I can!
There seems to be a big jump between the expectations of Saxon K and those of Saxon 1, which frustrated my oldest child. She especially struggled with the timed tests. (She's now using Saxon 6/5 in fifth grade, and doing just fine, so the frustration didn't last.) My second child was in public school for Kindergarten, so we delayed Saxon 1 until he was homeschooling in first grade. That track has worked really well for him, and he's in third grade using Saxon 3.
So, with those two experiences under my belt, and knowing my son's disposition, my plan is to do Saxon 1 at half-speed, taking 1.5 to 2 years to complete. My hope is to introduce a couple of lessons per week and to spend the rest of the time emphasizing the morning meeting, calendar work, memorizing math facts, and writing numbers. If we're moving too slowly, we can always pick up the pace.