I have several 8mm's in my gun room, including 8X57I, 8X57IS, 8X57IRS, 8X60S, 8X60RS, 8X64S, 8X64RS and 8X68S. I haven't gotten around to field testing the 8X64S and 8X68S, but they're pretty high on my to-do list. So far every one has proved more than adequate for white tails and I wouldn't hesitate to use the larger cartridges on elk/wildebeest size game.