I personally think you'd be better off using the 4-ohm taps.
However, I don't think it would hurt the amp to make the comparison as long as you keep to a moderate volume level.
Once you've made the comparison, if the 8-ohm setting sounds better to you, then use it. If not, go back to the 4-ohm taps. My guess is that the 8-ohm taps won't sound as accurate in the lows or the highs with your speakers; but see what you think and let your ears make the decision.
However, I don't think it would hurt the amp to make the comparison as long as you keep to a moderate volume level.
Once you've made the comparison, if the 8-ohm setting sounds better to you, then use it. If not, go back to the 4-ohm taps. My guess is that the 8-ohm taps won't sound as accurate in the lows or the highs with your speakers; but see what you think and let your ears make the decision.