According to the Boeing Flight Training Manual Vref 30(or 40)+5 (or relevant applied wind factor), is the recommended approach speed - for full manoeuvre capability at Flap 15 (Go Around) configuration. - I'm not sure what the relevant Vs factor above stall speed for either configuration is - perhaps someone has the figure to hand..!
One thing that is quite concerning to view is the high/low speed buffet margins on the -800 in ISA+ conditions. This has led to a few instances of high altitude stalling which have resulted in quite a few operators developing SOP's limiting flight crews to stay within the FMC calculated optimum Flight Level(s)
Cheers
ScottyD
