Why would GT5 need to beat Halo 3's opening week, its sales dropped off rather quickly and weeks 2-52 matter in this. Here's a bet, GT5 first year of sales after launch will exceed those of Halo 3. IE GT5 YTD > Halo 3 YTD. Winner chooses the losers sig and avatar for a month.

On the contrary. I have been following your responses carefully as well as Hyrukens responses to you. I enjoy a good debate as much as the next guy. Unfortunately for those of us viewing your debate, Hyruken is using logic and numbers and you're using nonsensical buffoonery.

If you can explain how a game with a lower attach rate would sell more copies than a game with a higher attach rate on consoles with an equal install base then I retract my previous statement referring to you as a buffoon.

Best of luck to you.

@Toefactor

You must be skipping over my posts. MGS3 4.02 million sales / 140 million user base. MG4 3.90 million sales / 21 million user base. Remember that MGS4 has only been out for 39 months. Looks like the sales were unaffected by the user base. Remember that GT3 was more than twice as popular than as MGS2 and GT4 was more than twice as popular than MGS3. You must really suck at following debates but the conclusion must be clear even to you. MGS4 was unaffected by the PS3's smaller user base. GT will likely be unaffected by the PS3's user base as well. GT is more than twice as popular than MGS. MGS4 has sold 3.9 million in only 9 months. If GT is more than twice as popular as MGS yet again then 7.8 million in 9 months is possible. If that's the case then 8.2 million in 12 months is possible as well. Please, actually read what I wrote this time, will you?

Thats' a Ferrari dude LMAO.....anyways, same day release of both games, I think Halo 3: ODST would sell more.

Everything you say is totally irrelevant to this thread. The OP stated specifically that he wanted to know what our thoughts were if the games released at the same time and both 360 and PS3 had an install base of 50 million. Therefore, the ONLY logical way of coming up with an answer is to compare attach rates for the Halo franchise vs the Gran Turismo franchise. 

Why you're even mentioning MGS or GTA games in your posts is bewildering to say the least. What it comes down to is this. 

Xbox360 at 50 million consoles sold + Halo 4 with a 25% attach rate = 12.5 million copies sold

PS3 at 50 million consoles sold + GT5 with  even a 10-15% attach rate = 5-8 million copies sold

The only way GT5 would outsell Halo 4 based on the OP's scenario would be for the attach rate of GT to be higher than that of Halo which it is not.

Now as for your bet, it's also irrelevant, but also unfair since Halo 3 launched with a 360 install base of 18 million where as GT5 will launch to a PS3 install base of somewhere in the neighbourhood of 25+ million. I think you should be giving Hyruken odds :)

@OP: It would pretty much be the best day in gaming, ever.

@Toefactor

Attach rate varies wildy from one installment to the next and is an extraordinarily poor way to determine the sales for the next installment in a series. MGS4 having a far greater attach rate than MGS3 should have made this fact so painfully obvious but somehow it didn't. This example is relevant because is shows how attach rate is useless in making predictions.

Of course attach rates aren't a perfect science. Never claimed they were, but for the sake of this thread comparing attach rates is the only logical way of making a prediction. What other possible way can you think of? "Errr, ummm I think GT5 would sell more cause GT games are teh 1337 pwnzorz lulz!"

In a nutshell, there is no perfect way of answering the OP's question, but some ways are probably more accurate than others, and both the Halo and GT franchises have a long sample list to base attach rates on. I doubt very much that either franchises attach rate for their next game will change dramatically.

Can you think of a reason why Halo 4 would have a lower attach rate than 25% or why GT5 would have a higher attach rate than 25%?

@Toefactor

MGS3's attach rate is 2.9% and MGS4's attach rate is 18.6%. I think attach rate is meaningless. I think Gran Turismo 5 will outsell Halo 3 because Gran Turismo 3 & 4 outsold Halo 1 & 2. I can make other points but this sums things up pretty well. GT is the more popular franchise and the size of the PS3's user base will likely do little to stop GT5, especially if Sony cuts the PS3's price (which is likely considering how far GT5 is from release)