Here is a brief summary for both
i5-3550P
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Faster 4 cores
Almost zero overclocking ability
No upgradability to Haswell or future chips (Socket 1155 has come to an end)
Low power consumption
Since it has no integrated graphics (P edition), if your Graphics card dies, you'll be left with an unusable system till you get a replacement.
FX-6300
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6 medium speed cores
Unlocked multiplier, very easy overclocking
Can upgrade to future SteamRoller chips on the same AM3+ socket
High power consumption
Althought the CPU doesn't have a backup integrated graphics, some motherboard do (not sure which chipset), so you won't be stuck with an unusable box if your card fails
However, both are more than capable of handling high end gaming, and as games slowly start using more cores (like crysis3), the FX-6300 should get rid of any gaming performance delta it has with the i5