Your data rate is determined by the condition of your line when sync occured. The max data rate is the rate attainable were you to re-sync at that point. Once synced your snrm will fluctuate and hence max data rate will also fluctuate. If you sync at a good time when your max rate is high, you will remain synced at that rate despite your snrm dropping (until a re-sync is forced if it drops too low) thus your actual will be higher than your max. Iam currently syncing at 53559 with a max attain of 50688 and an snrm of 5.8dB.