I must admit, I never answered a call when I had the 1.5GHz kernel loaded. I made a call and it worked fine.
But Wednesday night I opted for Adrynalyne's v1.9 kernel.
OC is fun...but the excess battery drain doesn't justify the "real" speed increase...I'm not concerned about benchmarks as I just want fluidity in the actual performance.
Haven't tried the 1.8GHz kernel yet...but I'm sure I will this weekend (just to play around)