Blacks are faster, they're the performance variant of the consumer WD line. Having said that, they tend to be a lot more expensive, often around 150% of the price of the same capacity blue. While they're decent HDDs, they're not massively faster than blues. Part of what you pay for is the longer warranty.
I was in the same position as you and ended up with a Seagate hybrid drive for my game library. I found it was actually priced slightly lower than the Black and for gaming - at least in theory - you often load the same assets repeatedly (like you die for example and have to reload the level), so the caching can help **at least in theory**.
Even if you never make much use of the cache, the firecudas are still 7200RPM drives at heart, so aren't massively slower than the Blacks anyway. I wouldn't pay a big premium over the Black for a Hybrid drive, but I'd certainly go hybrid if the price was similar.
Don't ignore the older Seagate Hybrid drives either that still seem to be kicking around for a little less than the newer models. Obviously if priced similarly the newer model is the pick, but if you can save a bit of cash it might be worthwhile.