In 2009, the price cut week accompanied a x2 to x3 lift in every world market initially, before settling to 75%, 60%, 50%, and then finally 35% for a couple quarters (most of the impact was in Nov-Dec).
In the USA the price cut came at the start of week five of September NPD.
Aug 2009 wkly avg - 69k
Sept 2009 wkly avg - 93k
However, there was no significant software in weeks 1-4 of September, so I think its reasonable to say that the transition in the USA was more like so:
69k-69k-69k-69k--Price Cut lift to 184k
October was then 507k, or an average of 126.7k per week (NPD probably had 140k, 130k, 123k, 114k), Nov had an average of 315k per week (much of it on Black Friday), and Dec was 762k per week. Normally Nov = 2x Jan-Oct monthly levels, and Dec = 2-3x Nov monthly levels. So without a price cut Wii probably would have gone 70k per week in Oct--> 420k per week in Dec (2.1m...it did 3.8m) instead of going 70k --> 762k per week (x11).
The price cut basically doubled seasonality in 2009.
In the Japan, the first four price cut weeks were 118k, compared to 64k in the last four 25,000 Yen weeks. The price cut also roughly doubled the seasonal increase in Japan from late September to the peak week - x19 instead of x8-9 in previous years.
Given a May price cut, the late seasonal lifts will probably be only 1.5x greater than usual rather than x2.