Sometimes when i do a TT and if i perform a fast lap, i tell myself : "Damn, this lap would have been a winner in a sl session, s**t !" .
I'm like Kanar here, i search for the ultimate lap ! And it's also possible to try some crazy tricks barely do-able on 5 laps
But both are great for big adrenaline rush !
And about consistency, after hours on speedlap, you can know every inch of a track and in fact only one lap can appear quite long in fact, with several sections that you have to think of ! So consistency can be improved to in practicing speedlap (but it comes faster with TT).
About TT, i'm quiet and concentrate during the four first laps, and i start to be very very stressed when the 5th lap begins, more stressed than on a great start on a speedlap