At 1+7 you will get some compensation with D23 but speed and shadow contrast will still be relatively poor, with an increase in graininess. Development times will be quite long - not necessarily a problem but something to be aware of. pH is not the only factor in determining the relative graininess of a developer. Is there a specific reason you only want to use two ingredients, why you do not want buffering, etc? What are your goals in terms of sharpness, speed, contrast, curve shape and graininess?