Wiki now says 1% TA and I have heard some testimonials from nonthf's backing this up. I have also heard a theory that it gives a % increase to TA, minimum of 1%. This would explain why some people (if they were thfs) would report 2.5%, however this is unconfirmed.
I remember the 2.5% triple attack rte being tested by divisortheory back in the day. Can't remember what the sample size was. Maybe one or two thousand swings.