C
Chris Angelico
Yes, I suspect it comes from people expecting too much consistency. If
something that has "conformance" is "conformant", then something that has
good "performance" must be "performant".
In a surprising coincidence, the word "performant" came up in a Daily
MTG article today:
http://www.wizards.com/Magic/Magazine/Article.aspx?x=mtg/daily/feature/278
Though it is used in double quotes to indicate that it's not exactly
standard English
Funny to see two nerdy interests meet!
ChrisA