1. The figures exported from the Speed Meter to a file are either bytes/sec or bits/sec, depending on what you set in Settings - Graph - Transfer Rate Unit. In other words, the values are plain values, not converted to KB or MB. If you divide by 1024 twice, you will get the same number as displayed. The reason the values are not converted is to enable charting, say if you wanted to build a MS Excel diagram, you would need the plain numbers.
2. There is no limit on the number of lines, but it looks like a speed test may occasionally get stuck and new tests don't run. We haven't found yet under what circumstances it occurs, though
one issue was fixed in version 6.1.1 - you may like to
update if you are using an older version. Otherwise you can simply restart NetWorx and the tests should resume.