Old school graphic design used D50 and a gamma of 1.8 (Mac's in general used to all be 1.8 back in the "they are better for graphics" day).
Now that calibration is to optmize the monitor so the ICC profile has to do less work.
The software also creates and ICC profile that tells your applications like photoshop or illustrator exactly how much color your monitor can produce so it can adjust the content to match what your display can do.
For games you want to have D65 and a gamma of 2.2 or preferably the sRGB curve. I also have a dell u2410 and game a lot on it, and don't find any issue with keeping brightness in the teens (16 right now). It's way easier on my eyes, high brightness causes eyestrain, but if you like it turned up then by all means turn it up.
Also there isn't anything that says you need it at 120cd/m for photography so feel free to calibrate at 200 or even 250 if you want. The thing is that in order to have accurate color, you can't have alot of ambient light and anything more than about 120cd/m will cause eye strain in a dim room.
CalMAN Lead Developer