I can see your point, maybe some type of distinctive outline (white?) around the words.
Either an outline or some other way to make it distinct.. for example making the words a solid red while the flames behind are a different color (yellow, orange, etc).. it would make the text pop out more and be easier to read..
1 and 4 are the best....3 looks 'too big' to me and 2 is just eh...but i voted for 4 cause it looked the 'simplest' and coolest...cause sometimes simplicity is best.
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