LUT (ROM) in DSP-Builder

Hello Alteraforum!

My current Design, for which I use DSP-Builder 8.0, includes several Look-up tables, for which I use the "LUT" block from the DSP-Builder blockset, Storage section.

For small LUTs, e.g. Address Width = 4bit, Data width = 5bit, I am inclined to implement them without registering data or address (because otherwise, I would lose speed and/or the control logic would get more complicated due to additional wait states).

Obviously, this is not a good idea for very large LUTs. So the question is, up to what LUT size would it be reasonable to not register data and address? In the DSP-Builder help for the LUT block, I only found this on the "use LPM" option:

--- Quote Start ---

Altera recommends that you turn on this option for large look-up tables, for example, greater than 8 bits. The input address is always registered when this option is turned on.

--- Quote End ---

Are these "8 bits" applicable to my question as well? If so, what is meant here by "8 bits"? I suspect the address width, but am not completely sure.

The device I am planning to use is a StratixII, the design should run at 100MHz.