given what gt5 will bring to fans of cars; nascar, wrc, over 1000 cars including the new supra, *top gear track, weather, damage and the ability to share lap viedeos, i would say:
europe: 4million (thanks to top gear)
japan: 1million
americas:2million
* top gear has over 350millions viewers world wide
http://en.wikipedia.org/wiki/Top_Gear_%282002_TV_series%29
if polyphony put in rthe tracktimes for the celebs and stigs, i think top gear will sell the following amounts:
europe: 5.5million
japan: 1.5milllion
americas: 3million
also, unlike gt4, gt5 will be the 1st proper full real driving simulator released on the console similar to gt3 on the ps2. i wouldnt be surprised if it does similar numbers!