With hobbit and it's cursed stock rear pulley I noticed a massive difference in acceleration particularly in the already miserable lull after the rpm drop and before the cylinder got up. It took a tuck at times to get it to actually gain rpm to hit more power. That was going to 2.75 gp1s. I could feel the resistance everywhere.
The top end actually wasn't as dramatic a change but the places where you were at the majority of the time were agonizing.