Not counting actual races, intervals that have paid the most dividends for me this summer are 4x15 sweet spot, except you start em with 1.5min vo2, do 1.5min vo2 in the middle, and end with 1.5min vo2. The sweet spot gives just about as much benefit as FTP stuff but also lets you do the vo2 on top of it. About as painful as 10x30AWC but last way longer...