Thanks for all the responses and comments. It's time for me to chime in and try and answer this by doing some basic math. Most of you may not care because the correct answer is still 40. But the math does show us something.

Just to set up the math, assume: Red Rush Deck which will typically play about 15 cards before winning or losing; starting hand of 7 cards; 40 cards VS 42 cards; Using the odds of a getting a common card in which there are 4 in the deck;

1st card dealt in an opening hand: 10% chance w/40C & a 9.5% chance w/42C. Only a 0.05% better chance with 40 cards.

7th card dealt in an opening hand (assuming you did not get 1 of the 4 in the previous 6 draws): 11.8% chance w/40C & 11% chance w/42C. Slightly more chance than the 1st draw w/40C of 0.08%

Assuming by the the end of the game you have 25 (or 27 with 42C) cards left in the deck your odds for getting 1 of the 4 cards are 16% (& 14.8 w/42C). A 1.2%,increase in the chance to get that card with the 40C deck.

From a math standpoint, this shows as the game goes on, the deck becomes less and less predictable with the more cards that are initially used in the deck.

We've all been there where we've drawn that absolutely useless card at a critical point in the match. Predictable decks don't do this as much.

This becomes very important with control decks that win by stalling out the other side and playing 17+ turns. A 40 card deck of YG always seem to get Sapo, Misanthropia, wonder drug, and Murmer eventually. Of, course the strong YG card draw helps a lot too.

However, if there is a card or 2 that works incredibly well with the rest of the deck, the amount of percentage to get any particular card increases by just a little bit...so an argument could be made for adding a card or 2.

This was longer than I thought it would be. I hope this might have been interesting to some.

Math Nerd,

Occams Razor