Using Pantone Tints on standard letterhead paper

I am looking for some help/advice regarding the use of tints of pantone colours.

I am looking to produce a watermark effect on the paper, thus I only require a small tint.

I have 2 colours to use, PANTONE Reflex Blue CVC and PANTONE Orange 021 CVC

What is the lowest percentage I can go? At the moment the Reflex blue is set at 3% and the orange is set at 4%.

This seems to give me the effects I need when printed on a inkjet (I know its completely different from a printing press).

Has anone else here produced a watermark using Pantone tints?

If so how succesful are they and what is a suitable level of tint?

Thanks

M