Before I begin please note I'm trying to look at this without bias. If you see bias please note it and explain why it may be bias.
I've been observing the architectures of both Sandy Bridge and Bulldozer lately. I mainly have compared the Sandy Bridge top 2600k (I know the 2700k is out...but the 2600k has been benchmarked much more broadly offering a better view of its potential.) and AMD's 8-core unlocked CPU, the 8150. I find something eerily similar between the two. Not the "You thieves!" similar, but the different road to same end similar. Take a look at Bulldozer's architecture diagram:
File:AMD Bulldozer block diagram (8 core CPU).PNG - Wikipedia, the free encyclopedia
Notice how you do indeed have eight physical cores. But wait, look again. Those eight cores are sharing the resources that four cores normally share. This is further shown in the official specifications of the 8150 shown here:
AMD FX-8150 "Bulldozer" CPU Review - Introduction & Specifications
Again notice the eight cores share four caches which are split among them. This is because Bulldozer consists of four modules, each one with two integer cores but other than that, each module has single shares resources. This explains why the 8150 performs nearly the same in games as an i5 2500k. But wait, the i7 2600k performs the same in games as the 2500k. Interesting. This is where the 2600k and the 8150 become eerily similar.
"But keyboard, you can't compare those CPUs in games, that doesn't use their full potential!" Correct you are good sir, Lets check out some multi-threaded goodness. Take a look:
AMD FX-8150 "Bulldozer" CPU Review - Page 10 - 3DMark 11 & Lost Planet
That benchmark shows 3D Mark 11, which is one of many multi-threaded benchmarks that is available there and many other sites (A google search away). Looks like the 8150 is close enough to the 2600k to be considered on-par. There is a one hundred point difference here and there but lets face it, the 8150 is cheaper. But what does this all mean in the end? It means the 8150 is a marketing ploy gone bad, or good if you notice they are sold out. AMD markets this CPU as an eight core and indeed it is. However at the same time, the 8150 is no better than a hyper-threaded quad core due to its design of sharing the resources a single core would share.
AMD has lost credit in my department. Not because I hate them, but they have gone to the dark side. The "oh may gawd look at all dem cores!" side. They are convincing people more cores + higher clock instantly equals better performance. Bulldozer is by all means a good sandy bridge competitor. Is better? No. Is it worse? No. AMD unfortunately provided their competitor a bit late in the race. Intel is already dancing at the finish line. Everyone wanted Bulldozer to be an Ivy Bridge of AMD, unfortunately its just another Sandy Bridge. Product wise, the 8150 is a great mid-way point between the 2500k and 2600k both in performance and price.
Did I look at this in all the wrong ways? Be sure to let me know by typing in capitals.