We experimentally study the modal interactions in mode division multiplexing (MDM) links supporting orbital angular momentum (OAM) modes of order zero and one. We use time of flight and channel impulse response measurements to characterize our OAM-MDM link and quantify modal impairments. We examine two OAM fibers with different index profiles and differential mode group delays (DMGD) between supported vector modes. Data transmission experiments probe the impact of modal impairments on digital signal processing complexity and achievable bit error rate for OAM-MDM link. We discuss in particular memory depth requirements for equalizers in separate mode detection schemes, and how memory depth varies with DMGD metrics as well as crosstalk level.