What's the first?

No risk involved, and a prediction such as the bolded is seriously no contest and is boring.

prob mario kart 7

Mario Kart 7 with 15.57 million copies. 

You're probably right, but for both franchises you are completely disregarding digital sales. I would guess that if GT Sport is as successful as you think it will be, it would be the best selling in the franchise. Not only because A ) Digital sales take up a rather big amount of games sales, but also B ) If it were to actual outsell all those Forza games, you'd have to include their digital sales.

Yeah, nope also the only way it will get even close to selling 13 million is if they bundle it to death (even more then the did with GT3).

Yes, which isn't saying anything considering no other 8th gen racing game has or will come close to GT Sport or Mario Kart 7

Correct which is why we're gonna stick to the physcial only approach. We'll never know Forza's digital sales anyway

Don't think so there buddy, every Gran Turismo besides GT6 has sold well over 10 million, and the first Gran Turismo on the PS4 will surely be no different. In regards to the bundling comment, it will obviously get bundled as all Gran Turismo and Sony games in general usually do, but bundled sales are still legit sales, contrary to your downplay

Forza 6 is just barely out pacing forza 5 when you align sells. So both games will end up around 2.4 million ish. Yet you expect 7 to do only2. You also expect all forza games to stop selling copies I guess. Your 10.2 should really be about 13 when these games actually finish selling copies. And that's also retail only. So u expect gran turismo sport to do 13 million retail total like 20 million(including digital). That seams pretty high sales for anyone to expect.

I had a good laugh

I don't think so. It would have to become the second-best-selling game of the series, which is a pretty big feat even on its own. I also have a hunch Sport doesn't have that appeal. I wouldn't mind being wrong, but I'm not too hopeful.