Sean I'd avoid the D7100 for sports shooting as it's AF system struggles with moving subjects especially in AF-C mode. It's noticeably poor when someone is walking/running towards or away from you and will happily snap while out of focus. Another issue with D7100's is sometimes (rare I admit) it just doesn't want to take a pic - you can point at a still subject (say 10 mtrs away), depress the shutter and the cam does errr….. absolutely nothing. On paper it has Nikon's 51pt all bells and whistles AF system but performance wise it doesn't live up to my other older Nikons.
If you decide on getting a DX body then a D300/D300S is still the way to go.
