I've tried the 5:1 thing for deep cranks and it doesn't work for me. I've fished a 5:1 and a 6:1 side by side with the same deep crankbait multiple times, and the 6:1 will get the bait deeper and get more bites for me every single time. You can always slow the retrieve with a 6:1 to work it over the top of brush piles. I know everyone fishes a little different but that is one recommendation that makes me scratch my head every time I see it. I have a nice Lews left handed 5:1 reel that I never use. Nice smooth reel. Just has no place in my boat.
Thats interesting, but we all know that retrieve speed can change day to day hour to hour for what the fish want.
I was catching lots of spinner bait fish last year, this year none, I realized last year I was using a spinning reel, so I tried my 5.3 baitcaster and boom caught spinner bait fish again on the first cast and any time I picked it up that day and subsequent days since. Sure I could slow down with my 6.2 but that isnt easy to do when you get fish one two three casts in a row, we all get a bit excited and want to snatch the next one. the lower ratio reels are another tool in the box. definitely not always needed but then again neither is 99 percent of the stuff in our boats...
2 lbs in line size will make more of a depth change than reel speed and will let it dive faster
I have 10/12/15 rods for crank baits and will tie the same lure on all three and let the fish tell me which they want, if none of those I grab the 5.3 ratio rods that have 10/15.