low light AF of D40 with Sigma 30/1.4

Hi,

I want to know your experience with the combo D40 and Sigma 30/.4 HSM in low light.

I currently have this lens in Pentax mount and the AF in low light is very slow. As this is my main lens, I consider a switch to Nikon, since the lens is HSM in this mount. Therefore, I expect it to be faster. May I be right? Can I shoot moving persons indoors in badly lit rooms without problems?

Another question: Is the AF of the D40 generally slower than that of the D80, or are they the same? The lower number of AF points does not bother me.

Thanks for your help,
Thomas D.