I agree that in the past (pre 0.142u4 hlsl mame) a higher pre-scale value was definitely needed to avoid a blurry image when upscaled to hi-res. But now hlsl will upscale the image itself and post-process it in multiple passes and the final output and effect will look better and closer to what you saw on the original arcade monitor when the pre-scale is set to 1 otherwise it is just a waste of potential to enable hlsl just for the scanline effects and saturation alone if the output is going to look like that.