Actually, there are limits mentioned in the FCOM (737NG), max speed for flaps 2 is 250kts and the flap maneuver speed is Vref 40 + 40kts. On Speedtape equipped airplanes you get those indications displayed directly as well. Had that on all -300s and -500s i've flown and of course on the NG it is standard anyway.
By the way, do some airlines require a direct flaps 15 to 40 jump during extension? We have to use flaps 30 inbetween there which makes it somewhat easier, flaps 25 as non-standard operation may be used.