Your GTS 450 DID NOT play Battlefield 3 with those settings at 1920x1080. Just tried it on my GTX 560 Ti. I got anywhere from 50 to 70 fps. GTX 560 Ti is more than twice as powerful as GTS 450:
http://tpucdn.com/reviews/MSI/GeForce_GTX_550_Ti_Cyclone_II/images/perfrel_1920.gif
Said that, you would get around 25-30 fps, which IS NOT playable at all. You should aim for 45-60 fps average, not 27.
Furthermore, GTS 450 is around as powerful as GTX 260:
http://tpucdn.com/reviews/Zotac/GeForce_GTS_450_Amp_Edition/images/perfrel.gif
And lastly, 1600x1200 is not small resolution. (1920 * 1080) / (1600 * 1200) = 1.08, which means 1920x1080 is only 8% larger resolution than 1600x1200.
In conclusion: no, he will not be able to play BF3 on high settings.
P. S. with AO and AA off, it's not high anymore. AO and AA adds much to graphics. Very much.