I do a little spinning with a top whorl. It is an Ashford. I took a class in Northern Wisconsin at a little yarn shop. She did not mention that the size of the whorl made a difference on the type of yarn you spun... but rather how you do with the stretching of the fibers while spinning.
She showed us a lace weight and a thick n thin yarn spun both with the same spindle. In the class I was really good at doing the spinning of a lace weight type yarn, but after I got home I was a little more of a worsted weight yarn when I was done, and sometimes, if I got lazy and was not paying enough attention, it was like a thick/thin yarn.
I don't know if this helps much. I do enjoy it and it is rather relaxing, but with three kids around (two mine and one I care for) during the day, and working part-time evenings, I don't have a lot of time to spin. I am looking forward to being able to purchase a wheel sometime and really get into it.