Mousepad - Its good... its a mousepad, what do you expect?
Keyboard - I own the Steelseries 7G and its by far my favorite mechanical keyboard I've used, the 6GV2 is the 7G's little brother. I am a fan of black switches, mostly because I'm a very heavy typist and the rest of the switches are too light and subsequently too error prone with very high actuation points. You should try to see what kind of switch you like as it will be different from person to person, of the people I know with mech boards, 2 have blue, 1 has brown, 1 has black. One thing to note about the 7G and 6GV2 is that they have slightly altered layouts, the 7G has a shortened backspace with the pipe key moved up, the 6GV2 has a shortened right shift key with the pipe moved down. All in all its a rock solid board, braided cables and a steel backplate, you could beat someone to death with it, plug it in, and type an email to his mom on all the same board. For budget minded individuals, I also often recommend the CM QuickFire Rapid/Pro.
Mouse - The Kinzu V2 is a solid mouse, well built, braided cable etc, but in terms of features, its ultra basic. A max cpi of 3200 and no side buttons is a odd thing for a mouse of this price. Its by no means bad, and if your in the market for a solid yet simple mouse, this may be one of the best options, but understand that many other brands offer similar build quality and a good number more features for nearly the same price. The Cooler Master Sentinel is insane for neary the same price, check it out sometime, the damn thing has its own scripting language.
Headset - I own two pairs of these, I think they are pretty sick, good look, solid sound and the mic is very clear. With that said, I'm am by no means an audiophile, I've been handed $700 headphones and not really been able to tell much of a difference. This headset is geared towards games though, keep that in mind, I find music sounds good in them, but games sound great, I've actually caught myself thinking noises from inside games were actually coming from behind me. Not that I'm damning the opinions in the comments above, I'm saying these are good products and if you've got your heart set on you probably won't be dissapointed. One thing to note, I've found they will break every 1 - 2 years of heavy use, and while they are near impossible to open up and repair, SteelSeries has just been willing to replace them for me time and time again even though I'm well out of my warrenty now, they don't even ask for my receipt anymore.
Monitor - I'll echo the opinions of the comments above on this. Do you even have a system that can play games at 120FPS? Coming right down to it, I find most game that acheive above 30FPS I dont' really notice the framerate, so 120MHz would be overkill to me, but I know people who have (tried to) justified their purchase.