D'rye Stout / Flakes or malt?

Hi there!
Recently I began a series of stouts. The idea is to keep a big part of the recipe identical, but change only one factor, and this factor is a non-barley cereal.

Here's the base recipe, it's a kind of a Dry Stout.

75% 2 row
5% Chocolate malt
5% Black Malt
15% other cereal
Nugget and Fuggles for about 60 IBUs
Around 5% ABV
Yeast: Not defined... might change according to the cereal. It is not a really scientific test, we want to brew good beer at first

First, we brewed an Oatmeal Stout. So, the 15% was roasted oat flakes, and we pitched Whitbread Ale yeast from Wyeast.

Now, we're at next: D'rye Stout. 15% of rye might bit intense, but, hey, we stick to the game, and we'll see. My question is: Flakes or Malt? Is there a difference in flavor? First I was thinking half/half, so we keep a good mouthfeel. What do you think?

And for the yeast, what would serve well that crisp dry rye taste?

Rye in any form will give you plenty of mouthfeel; it's loaded with beta-glucans, aka soluble fiber. If you use malt, grind it finer/twice, as it's smaller than barley. It's also huskless, so some rice hulls would be helpful, but not essential. WY1335 is my stout yeast of choice, but you could probably use almost any American or English yeast and make good beer. It's mostly a question of how attenuated you want it.