I'm not surprised that threaded perl builds are slower. I know. I also know that the impact is much less now in more recent perl builds that it was in older perl versions. I can see on a day-to-day basis what the impact is of threads vs non-threads in my smoke status. Today it shows threaded is 5.3% slower than non-threaded. Look at the bottom.
I hereby would put the word "significantly" into a bit of a context. I still think that 5.3% is significant enough to not want a threaded perl build, as I NEVER ever saw the need for threads.
With more and more (useful) perl applications actually using threads (e.g. Padre won't even run without them), I can see people wanting them. For me any app requiring threads is reason enough to not even try it.
Enjoy, Have FUN! H.Merijn
