I know that Merchant Pot Turbo focuses in on Magical Merchant, but not everything deals with having a greater chance on getting that one card. For example, for a 40 card build, the probability of getting Magical Merchant is:
[1 - (27/40)(26/39)(25/38)(24/37)(23/36)(22/35)] => around 92.3%
In regards to a 60 card build, the probability of getting Magical Merchant is:
[1 - (47/60)(46/59)(45/58)(44/57)(43/56)(42/55)] => around 78.6%
From logic, obviously the 40 card build is better at getting Magical Merchant; however, whenever I get a problem of getting hand clogged by having 5 ways of getting Merchant, then I fail to get the fatal blow in that match, and the match drags on into my opponent's victory, since I would have nothing left (besides the Manticore of Darkness where I discard a Beast-type monster, but that's irrelevant if your opponent already blasted it by a Black Rose Dragon destruction effect.
Not to mention, Six Samurai being able to roam around freely, being able to utilize The True Six Samurai - Mizuho's effect to waste whatever defense you have, and when I mean defense, I mean the only move that you can make really with this deck. Without being able to use Magical Merchant, the deck becomes dead in the water.
There is a plus side though. By being able to decrease your chance of getting Magical Merchant slightly, you can add more cards to your deck that can defend you, just in case, the mill of Magical Merchant goes in your favor.
...Not to mention, having 57 monsters in your deck, chances are that you would mill about a quarter to a half of your deck at times. (Sometimes, you get Pot of Avarice early, which makes you wait a couple of turns to get a good mill.)
Searching out Magical Merchant is no problem. You have Gokipon, Danipon, Rai-Mei, and Sangan ready to search him out. So, in total, if you add 3 of Gokipon, Danipon, and Rai-Mei to your deck, you'll have 10 searchers for Magical Merchant.
So, in short, it all depends on the mill.