do keep in mind that the m50 has perhaps the smallest soundstage of any headphone in your budget. it is small even for being a closed can. this means that all sound will be rather up front and sound close which is why it usually is not the first pick for gaming (open cans are preferred generally). also of note is that you can get open box m50s on ebay for $99 but brand new or about $110-120 not open. the m50x version is rather overpriced for what you get as the only real difference is removeable cables.
i personally own (and have owned for 4-5years) an m50s (straight cable) so if you had questions about it in detail i'd know and you can ask. i've used them for music, movies and some light gaming and while i do very much enjoy them i realize where they might not be quite as good in some areas as others (but i accept that since i bought them mainly for music, isolation and i required good bass).
you want deep bass but something a little better than an m50? look at the dt770pro 80. it may be a bit more than your budget but it has a wider soundstage than the m50 so a bit better for gaming though still closed with overall somewhat better audio quality and much more comfortable design. it performs best on a decently powerful soundcard though but should be playable on onboard (though you'd want an amp or soundcard eventually down the line)
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the hd598 you listed above is rather neutral sounding. it has a wide soundstage, good clarity and is typically considered one of the better headphones for gamers though your insistance on "good bass" levels throw it out of the picture.