Difference Between Kinds Of Specification Marked Cards
Standard, Large or Magnum Index refers to the size of the numbers and pips (suits) on the card. Large (Jumbo) index cards have larger, easier-to-read numbers and suits than Standard (Regular) index cards. Large Index marked playing cards are good to use on large oval tables because it is much easier to see the board cards (Flop, Turn and River) from the end seats. On the other hand, Large index cards are worse as hole cards (down cards) because you have to expose more of your card to see what it is.
Magnum index cards have even larger numbers and pips than Large index cards. The nifty thing about Magnum Index cards is that they have huge numbers and pips that can be seen from across the table but they also have smaller numbers and pips in the corners of the card, allowing you to simply flip up a corner of your down-card to view it.
Remember that it may be difficult for the players at the ends of the table to see the board cards (Flop, Turn, and River) especially if the overhead lighting is inadequate or the eyes of player are aged. You might consider using Large or Magnum index cards to make it easier to see the board cards, much depends on your players and your lighting. You could, alternatively, use regular index cards and ask the dealer to announce the cards as they are shown.