Here's another cautionary bit re relying on calculated projections -

Yesterday I did my hardest/best 5 min interval in terms of watt output. When that number get's crunched into a calculation using my older outputs for longer intervals, the net result is that the calculated FTP goes down - you might think of it as more work in the longer interval is attributed to my increased anaerobic output.

Did my FTP really decrease over the last month? Maybe, but I don't think so. More likely, I've gained across the board and this is an artifact of not having done a long interval that shows this. (My weekend cross races are not done with a powermeter, so I'm not getting data from these 40-45 minute efforts.)