I'm in the printing field(inkjet), even tho the file is 300dpi, the printer machine's printhead and setting still determines the final quality, even that generally 200dpi for poster is overkill, you won't notice much of a difference starting at 150dpi onwards.

I bet the BF3 local posters won't reach 300dpi.

Well if you can find hi res BF3 poster on the net, the more hi res, the bigger you can print without it getting blur.