Rather than a bunch of models or sprites, have them in bands in one single model. For best performance and the most detail, have your single model between 2000 and 5000 polygons. For 2000 polygons, you could get 1000 "ribbons" of grass. When criss-crossed, by duplicating the model, you could have enough grass to cover a 250x250-foot area when each ribbon is spaced 4 quants apart with a 16 quants per foot map scale. With such a setup, you could get 100 times the rendering speed than if you used tons of sprites or low-poly models. Want an example of this grid design?