21 farms pretty muched "nailed" the answer as far as I'm concerned. I've been experimenting--and changing my mind--about this issue for 20 years, so I have just a couple of additional comments. First, since I really started getting into square-bill fishing, I've read that a lot of guys feel the "need for speed" when deflecting these baits thru cover, so I've started experimenting with faster reels and found it's pretty hard to adequately "burn" a bait with only 20-22 IPT (like my 5.0 reels). I also like a faster retrieve when throwing lipless baits--especially in clear water--and since there's much less drag on the bait, it's a piece of cake. Although I still like using the slower reels for all my baits in heavily-stained water (to help me slow down a bit), the final consideration I struggle with is adequately handling a big fish coming at straight at me without being able to take line up quickly. Once you lose a good fish that way, you start 2nd guessing your slow-reeling equipment. It's all compromise and trade-offs. So to better control a fish under these circumstances, I don't want a slow reel on a SHORT rod, so my 6-8 square-bill gets the "faster" reel. I actually use an old Curado 3.8 for my deepest divers. Matched with an 8 foot rood, I at least have a chance of managing any slack line when playing a fish.
What's the point in having a hobby if you can't enjoy "over-thinking" and "over-analyzing?"