A suspension fork generally adds a few pounds. I wouldn't be terribly concerned about the weight, although having a cheap suspension fork generally isn't a good thing. Stock MTB tires definitely will slow you down too. The FX is lighter than the DS. Also, the FX has a short top-tube, while the DS has a fairly long one. As much as a FX seems like a perfect bike for me, I hate the short top-tube on it, but the DS feels great. If you know what you prefer in a frame, I'd use that to decide. If you go for a DS, I'd either go with the 8.1 to get the rigid fork, or 8.3 or higher to get disc brakes.