I've never tried the others, but I've had the same M50's for years. They'll last you forever, so just cough it up IMO.

How would you say the M50 compares to the AD700?

No idea, but be aware that the AD700 seem to be open-air headphones from what I'm reading and M50's aren't. That means you'll be able to hear everything going on around you with the AD700's and you can't hear shit with the M50's. If your gaming space is noisy then you wouldn't want open air I think.

you shouldn't be asking about headphones here. go ask for advice on head-fi. tell them your budget, location, what kind of music you listen to, etc.

AD 700 is really really good. I tried the q701 as an "upgrade" and it was awful in comparison.

I'm talking about ingame positioning.

the M50x already arrived and I'm loving it. It really blocks out most of the external noise, I can hear myself breath, which is awkward and annoying, but as soon as sound/music is playing it's fine. I also find it very "gripping", or I must have a fat head. I can't keep 'm on for hours, I think it'll need to settle.

I bought some m50x's the other day and I'm really impressed. I've used sennheiser hd580's for over ten years but I've only just realized how inappropriate they are for gaming. Closed back for gaming is definitely the way to to, it really helps you focus. I also love how they come with three different cables, so I can use it on the go with a quick cable change over etc. they sound awesome through my iPhone 5s :)

I think for gaming the bass is a bit too heavy by default. I've set my soundcard to "soft", which drops the bass a bit and ups the treble.

you should get the Sennheiser HD 280 Pro. around 100 USD, great sound, comfortable, and durable. what more could you want? i guess they're twice the price of the ATH-M20x, but i'd say they're worth it.