The Impact is phenomenal and set the standard for 100 yard competitions. I have two of them. If you buy an Impact, I hope you have patience with o-rings, it's got lots of them.
Is it more accurate than a Royale? with a .25 pellet, probably depends on the pellet. Do you shoot the 24 grain or 34 grain? Impact will probably do better with the heavier pellet, but not so sure about the lighter pellet.
To be honest, I think with both of them, the wind read is more important than the negligible improvement in accuracy.
Get whichever you want, I don't believe there's that much difference in accuracy!