GTX660 or r9 270 with 400W PSU

[pomelo]

Got an old computer that I'm thinking about upgrading. Currently it's using integrated graphics(with Intel i5-661 CPU)) so I thought a dedicated GPU would be the best alternative. However, it only have a Corsair 400W PSU which limits my options. I found the Geforce GTX660 and slightly more power hungry r9 270 which as far as I can see only requires one 6-pin extra power connector.
At the moment I don't want to mess to much with it and change power supply. So I'm wondering if either would work or if it's better to get one or the other?

 

[Sample_Text_420_Blaze_It]

I would definetly get the GTX660, UNLESS you go for games that actualy have the AMD software. ( similiar to DirectX )
Than I would choose the R9 270X above the GTX660. AMD GFX's perform better than nVidia GFX's if the game contains AMD software. Look at Battlefield 4 for an example; GTX770 blasts the R9 280X away, but when it comes about Battlefield 4(the game runs AMD software) the R9 280X outplays the GTX770. As I would say, look at which games you want to play, if that really doesn't matter at all... go for the nVidia!

Regards,
420

-QUICK EDIT- The AMD software is called Mantle.

 

[Calvin7]

Power Requirements:
GTX 660 (All) / 650Ti Boost:
Minimum of a 450 Watt power supply
(Minimum recommended power supply with +12 Volt current rating of 24 amps)
An available 6 pin PCI-E power connector

R9 270
Minimum System Power requirement (W) 500W
Extention Power Connector - One 6-Pin PCI Express Power connector

 

[huilun02]

The GTX 660 takes 10W less at full load according to official TDP. It outperforms the 270. That makes your answer pretty obvious.

By the way Mantle has not been released yet. No user/review benchmarks so far. Battlefield 4 will be the first game to be using it.

As of now here are benchmarks of the game without Mantle.
http://www.guru3d.com/articles_pages/battlefield_4_vga_graphics_performance_benchmark,7.html

Yes this particular game favors AMD cards.