I'm working on a 6 foot 4 medium heavy baitcaster. I'm trying to decide on guide sizes using Fuji LN and L frames.
My options are:

6 (x4), 7, 8, 10, 12
6 (x4), 7, 8, 10, 16
6 (x3), 7, 8, 10, 12, 16


This decision would be much easier if a size 14 do exist. I know I am being too particular with this, but it can't be helped. What are your opinions or experiences on baitcasting guide sizes?

10, all 6s. This is for a standard bass small palmed bait caster.

I prefer KW’s and will do 7, 6, then all 5’s, or 5-1/2’s. Your “choke” guide is technically the level wind guide on a baitcaster, so I see no need to go any larger than a 7, especially when using a low profile reel. My preferences developed from use, not building, if that matters.

You don't need all those different sizes. Use a butt guide and then make all the runners the same size. Better, straighter line flow this way.
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Fuji RV6, then whatever size you want to the end. The lighter the better for recovery speed. I use RV6 then two or three KB5's then KT5's to the end. Or even size 4 runners when I feel like it. They all work with the knots I need to pass.

LN 10 at about 20" from the face of the reel. LN 7 next in line, probably around 8" in front of the LN 10. But that distance could vary based on what static guide placement would dictate. Then whatever size L guide runners you decide to go with after that. I personally would go with #5's.

The only guide I wouldn't place using the 2 line static load guide placement method is the LN 10 butt guide. A number 10 either LN or KW, (they're almost identical in height) is all you need as a butt guide. A 12 or 16 is not needed at all. And as has been said, you don't need a whole lot of different size guides on a bait casting rod, but if you want to, simply because it looks right to you, you could go with an LN 10, an LN 8, and then an LN 6 and then your running guides. It's not at all necessary, but it's not going to kill the performance of the rod, as my guess is with a rod that length, it's going to be used for cast and retrieve techniques, so the extra weight of the additional double foot guide isn't going to hurt you.

Also, based on my experience, I would caution on using a 7 as your butt guide if you're using heavy, stiff line. With stiffer line a guide of that height could lead to line control problems on the spool. Meaning it could cause a backlash to start more easily. I say this based on my one casting rod having a KW 8 as the butt guide. When I use 10 or 12# fluorocarbon on the rod it casts wonderfully. When I have gone to 20# fluorocarbon on that same rod, I have to be more delicate with line control on the spool.