It'll beat the Prologue and PSP game. No doubt this game was a sales disappointment, but it released at the worst possible time. I'm not sure why people keep dooming and glooming the franchise.
Hold your horses! the game is still in the top ten in the weekly software charts.
I would not say it will break records but do not undestimate GT (and PS3) legs.
They will probably sell this game as the main GT/driver sim for the PS3 for the next 3 years in bundles (with TLOU for instance). It's still the best racing simulator (next gen included). The game is filled with content, the driving is near perfection and visuals has this next gen feeling (1080p-ish) .
GT4 sold 30% less than GT3. I predict that GT6 will sell comparatively the same versus GT5. So GT6 will sell about 6 or 7 millions copies when it's said and done.