A quick search shows that the fi-7160 has a CCD image sensor while the newer fi-8170 has a CIS sensor. I'm not sure how much of a difference that makes. PC Mag says that the fi-8170 is superior to the fi-7160 in every way.
Both of those are high volume scanners, so if you have A LOT of magazines to scan it might be worth getting the 8170 as the consumables (rollers and wheels) will last longer.
Looking at the scans produced by my fi-7160 using the ScanSnap for fi Manager program and comparing them to the ones Phillyman spits out using his ix500, I honestly don't see a difference in quality. So you might want to consider the ScanSnap ix1500 if you don't have hundreds of magazines you plan on scanning.
fi-8170 review
ix1500 review