Dell T710 Memory configuration with mixed Quad and Dual Rank RDIMMs

Hi all,
I've done what I'd like to think some pretty serious reading up until now... though have yet to find the answer to my question.

I have just purchase a T710 server with dual L5630 CPUs.  Being a T710, there are 18 ram slots and based on the Intel 5500, I fall under the 8 ranks per channel ruling.  I need I am trying to purchase ram economically now... as in 8 x 8 GB DR sticks now... another 4 x 8 GB sticks later, and then would like to know if I can add either 6 x 16GB QR or 6 x 32GB QR sticks (when available) at a later date.

I have read that the DR DR DR combination is ok, as is a QR QR combination... though can't find anything about QR DR DR.
To my understanding, this would keep to the 8 rank limit and in theory work, though for some reason I haven't been able to find any reference to this particular configuration so thought I'd ask first.

Has anyone tried this combination or know if it works?

Thanks in advance,
Tony