Thanks, all look great...I like #3 & #5 best.
I like the "R" on 5 better without the flame image, try removing that on #3 with the same long "R" as #5. I like the clean "Y" better on #3, try that revision on #5. Also, try making the 64 continuious flowing without the break for both. Then maybe try outlining 64 in white to make it pop and see how that looks.
I like that you used a different revision in the spelling in #7, just not crazy about that one.
Try it as:
SIXTY4
60FOUR
64
SIXTYFOUR
Thanks again!