Size 4 to size 5: when did you transition?

DS is doing well at potty training and I have to make a decision on diapers. I ended up with way too many diapers stashed away based on good sales. He's wearing a diaper at nap and at bedtime but I use the same one if he happens to still be dry when he wakes. I'm running out of the current box and need to decide if I should move up sizes or not. I could either open a box of size 4 (152 or 192 count, so a couple month supply) or a box of size 5. I know it's technically possible to not use up a box of diapers but I'd rather try to resell the unopened boxes than have him seriously outgrow the diapers we are using before we finish the case. DS is 2.5 years, 28 lbs, and tall and lean. It would be helpful to know when others moved to size 5. He isn't a heavy wetter overnight so I'm mainly worried about the diapers physically getting too small for him. I don't think DD ever made it into size 5 so it's unfamiliar territory for me.

ETA: if it makes any difference I have two large cases each of size 4, size 5, and size 3-4t easy ups.

We moved to size 5 around that size because the 4s were too shirt on the rise. I'd crack open your box of size 5s or just switch to buying smaller packs at Target or similar. I'm guessing your days of naps are numbered so you may find you're down to one diaper a day shortly.

My kids have never worn size 5! Ds2 is 26 lbs and still wears size 4. I can't remember my other two kids stats, but DS1 was probably 27-28 lbs when he stopped wearing diapers except overnight. I did move to size 2T pull-ups before switching to underwear.

I'd do the bigger size.

My DD2 is only 26lbs and has been in size 5 for a while. I think a bigger diaper is easier in many ways and gives more height. My DD1 transitioned out of diapers quickly after being potty trained and insisted on pull ups (easy ups) for bed time. She didn't need anything for naps.