Stats : Moves ratios?

How important is the existence of five stats + Hx, instead of say, 4 or 6 stats, with or without Hx?

Is there a ratio of

Stat:Moves built for a stat

that applies? 

i.e. if I wanted to have 4 stats an no Hx, should I also expect to have fewer moves?

Been thinking about this - I think that there's a point where fewer stats does NOT indicate fewer moves, but there is no visible ceiling apart from "how many of my stats do i care about as a player," which I suspect tops out around 7.

The hack I've been working on has four (4) stats plus a 2-box harm meter. The are currently only four basic moves, with only act under fire having a direct analog.

There were five but the fifth basic move was weak and was the wrong way to address the theme. Hold economies are a strange beast and I wanted keep everything dead simple.

AW has five stats (six with Hx) and eight basic moves (plus peripheral moves).

How I did it was to collapse +sharp with +wierd and/or +hot. I took out seize by force, seduce or manipulate, read a sitch/person and heavily modified open your brain; I added a social exploitation move but it works differently than seduce/manipulate and looks a lot like deep brain scan.

After Dungeon World originally had on basic move per stat (for 6 stats + Bond/Hx), I realized that the number really isn't important. Make every stat a distinct thing that characters can be (or not be). Make every move a clearly distinct thing that happens in the fiction, and which has a clear mechanical effect. The absolute numbers don't matter.

At least up to a point. If you have more moves than the players can keep track of, or stats that don't clearly do anything, that's a problem.