...at the moment.
My ideal:
27" - i7 - 8GB RAM - 680MX - 256GB SSD (hopefully that will be an option)
Dont get your hopes up. Yes i7 has bigger cache but mostly, you are better off getting SSD for that quick swapping pricewise.
Hyperthreading has been around for 10 years and it still has mostly niche uses. Unless youre transcoding lots of video daily and the longer renders cost you money, I dont see a reason shelling out extra for i7. Get Fusiondrice instead, that is something that will be evident in day to day use, with i7, those extra "cores" will be idle for most of the time.
It is a marketing thing to get more money out of you, yes you get more power but unless you are very specific kind of user you wont be using it. Same goes for Xeon processors.
I5 is perfectly fine for HD video editing and gaming, if you are someone who earns money with the system, those extra 20 minutes ripping your DVD might be beneficial. Many video pro's invest rather in storage because most of the time, you leave rendering for night, then it doesnt matter.
PS I realize there are more uses for i7 than for video production, its just sth Im familiar with and decided to share my perspective. I feel like lots of you just want to boast with i7 iMac.