I'm printing some banners and business cards with variations on a single design (banners coming from two different places, cards from a third place). The design has some very light grays in it: 4% 7% and 15% K. 

For the banners it's possible for me to add a spot colour. So I am wondering, is there a better chance of the light grays showing up properly if I:

A: Set all the greys to be tints of Pantone Black. 

B: Set all the grays to be tints of say, Cool Gray 3. 

C: Set the very lightest gray (4%K) to be Cool Gray 1 at 100%. And keep the other grays (7% and 15%) as process tints.

D: Stick with the process black tints. 

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I'm designing the banners in Illustrator. The material is fabric for one and vinyl for the others. Unfortunately I think its too late to get physical proofs made. 

Thanks very much, 

Conor