As for your question around turbo-boost technology...
The processors you've identified will all "go turbo" in the same scenarios (given identical conditions). The only difference is that the task you're doing at the time will complete or perform *up to* 15% faster on the 2.8GHz.
However, few programs/tasks do not utilise multi-threading nowadays, so you'd seldom see a 15% difference - more likely 5-10%. The more cores in use, the more restricted turbo-boost technology is. If it raised all four physical cores to run at 4.0GHz, your processor would likely self-combust in seconds.
Games were always a good example of where turbo-boost really helps. Traditionally, games haven't made use of multi-threading largely because of the "unknown" nature of them - you could turn left or right at any time, and the computer cannot predict. Processing every single possibility would be far too much work for consumer-level processors. As such, you cannot split up the processing of the game logic and run it in parallel, you have to just run it sequentially on one thread (over-simplified, but you get my gist). So, when you're gaming, the processor can under-clock three of your physical cores that are just running background tasks, and boost the remaining one up to ~4.0GHz to run the game as fast as possible. It will maintain this dynamic configuration until thermal throttling kicks in, where your boosted core's clock speed will start to fluctuate to avoid overheating.
Video rendering is a great example of where turbo-boost doesn't really help. When you're rendering a video, your computer already knows what the next frame is going to be (the exact opposite to gaming). As such, your processor can break down the rendering task into smaller tasks and distribute it across its cores. It will even virtualise more cores and utilise hyper-threading to complete the rendering task faster. In this scenario, your processor is running extremely hard on all four physical cores plus up to four more virtual cores - turbo-boost will be *heavily* restricted in boosting clock speed. There's simply too much heat already.
