Its stated on here to only have 275 knts cruise speed but several sources say closer to 300knts.
http://www.airliners.net/aircraft-data/stats.main?id=386
http://en.wikipedia.org/wiki/Yakovlev_Yak-40
Also janes all the worlds aircraft. says around 295knts
Max cruising speed (295kt) is not the standard cruising speed.
https://www.airwaysim.com/forum/index.php/topic,41739.0.html