Cores don't really work like that.
Think of the load your processor needs to complete as a bookshelf. The more things you're running, the more books you're stacking on to the bookshelf. The way cores work is that you're basically adding more bookshelves and taking books off the first bookshelf and distributing them amongst the other shelves. In theory yes, you can run more with more cores, but the programs won't necessarily run faster depending on if they have multi-core support or not. Some programs are developed to run on two cores, and they'll continue to only use 2 cores even on a 4 core processor.
As for raw processing power, games aside, you will get better performance out of the i7. The reason people tell you the i7 isn't worth it for games is that games are, as I mentioned previously, generally limited to 1-2 cores. Getting an i7 for that is overkill. The i5 has great single and dual core performance without the i7 overkill which is why it's the premier choice for gamers.
