As you probably already know, the point of getting a monitor with a higher refresh speed than 60 hz, is to experience games above 60 fps. Reaching the monitor's limit (120 or 144 hz) is very hard to achieve, and in some games (Crysis 3, Farcry 3) modern dual GPU setups struggle to run games past 80 -100. With your setup, you should be fine for BF3 (it came out in 2011). As for monitor choice, there is not much difference between 120 and 144 hz (24 hz difference). In all likelihood, the 120 hz will be cheaper, and like I said earlier, many games struggle to go past 100 hz maxed. 144 hz would seem like a waste of money to me, but if you find one at a good price it might be worth it. 120 hz seems like the better, more economical option at the moment.