Fit and feel is most important. A 17.5" GF should be fine for you, it just needs to be fitted properly. Fisher uses "Genesis Geometery" which among other things, has a longer top tube and shorter stem. You can safely put a size longer stem on to give yourself a bit more room, or slide the saddle back a bit on the rails. I find GF bikes to be a little too twitchy in the steering department, but a lot of people like it.
The Specialized is a more all-purpose bike, really. Fairly neutral, easier to ride, no wierd angles to account for in things like a new fork (the Wahoo uses Fisher's new offset crown thing....as of now, makes it difficult to replace a fork)
Otherwise, componentry is about the same level. Neither is going to be a true trail bike without some tweaking, but they are classified as recreational. I wouldn't attempt much more than what you have planned, but unless Iowa sprouted a mountain or two since I was there last, that really shouldn't be a concern.
The Specialized is a more all-purpose bike, really. Fairly neutral, easier to ride, no wierd angles to account for in things like a new fork (the Wahoo uses Fisher's new offset crown thing....as of now, makes it difficult to replace a fork)
Otherwise, componentry is about the same level. Neither is going to be a true trail bike without some tweaking, but they are classified as recreational. I wouldn't attempt much more than what you have planned, but unless Iowa sprouted a mountain or two since I was there last, that really shouldn't be a concern.