The 3.2GHz refers to the base clock, while the 3.7 is the turbo. As far as the "x" on the package I am unsure. The Athlon x4 740 is definitely not overclockable, and seeing as how there are no Anthon 740x chips it is safe to say that you have the Athlon x4 740. If you want to make double sure just look at the specs on the chip itself.
Edit: you could be referring to the model number, which is AD740XOKHJBOX for the Athlon X4 740
Edit: Just so your aware max turbo refers to a mode in which the CPU diables some resources, i.e., core, threads, other processes for a temporary increase in the base clock. This is useful for CPU intensive tasks such as gaming and has nothing to do with overclocking