Which water pump?

I think A/C equipped cars had a different (heavy duty) water pump. I just replaced my water pump with a good local parts store one, not a 90 day warranty part. I noticed the one I took off was an 8 blade impeller measuring about 4 3/8". The "good" one I bought was a 6 blade impeller measuring about 3 3/4". Apparently they aren't all created equal. I would shop around if I were you.