I would absolutely go with the Game One, picking between those two. It’s a time-tested headphone design with an amazing mic, and $150 is a pretty good price. It’s essentially a pair of 558’s with a broadcast quality mic attached. There’s nothing for me to criticize there. I’ve thought about reviewing them in the past, but my entire review would be “it’s a pair of 558’s with a broadcast quality mic attached,” haha.
I’ve not used the GSP 500 but I’ve used its older siblings. Unless you really think you’ll need the headset adjustment feature…you’re getting nothing extra or special for double the price. Plus, at $300, you’re approaching prestige headphone territory. Things like the HD600 are available in that range, or you could buy some DT990’s and an incredible standalone microphone.