At long range the times are similar, but at short range, BBs from a more powerful rifle will get to you faster. When I was playing with low power AEPs, it would often happen that I would shoot first, the other player would shoot, then I'd get hit first, then the other player got hit. Still a double kill, but he/she had a lot more time to try to dodge.
At long range, it doesn't matter much, because there's an exponential somewhere in the equation for friction, a faster BB also loses speed faster. Then you have to take weight into account, because heavier BBs conserve speed better and eventually overtake initially faster but lighter BBs... but anyway, there's already plenty of detailed posts about this.
Keep quiet. Sound travels faster than BBs.
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