I get 1-2 SST sessions in a week. Almost always a 2 hrs @ 90-91% and maybe a "one hour intro" to a long ride @ 93-94% threshold. 2x20's are rare in my program. I can only do 2-3 weeks with 2x20's in the weekly plan before I start dreading them.

My favorite is still 2 hrs @ 91% with 3-4x4 minute hill intervals @ 120% w/20-30 sec recovery before getting back in the SST groove @ 91%.The hill intervals give your legs the perception that 91% is really not that big a deal. (edited to add that I space the 4 minute intervals to whereever it is convenient on the route)