I was thinking I was going to get a R9 290X until I started reading around, and noticing my CPU will be bottlenecking a 290X, so which R9 is for me? 280X? 270?
I don't think I'm going to need TrueAudio, just mainly interested in maxing out the CPU and MANTLE.
The system is in my sig.
There will be a slight bottleneck on average but not much overall for the GPUs you listed. In GPU demanding games such as Far Cry 3, Metro games, Crysis games, you will be more or less GPU limited.
In some sections of the game you may not get 100% of the performance of R9 290 but that's where overclocking your CPU to 3.8-4.0ghz comes in:
http://www.techbuyersguru.com/ochtgaming2.php
A more serious CPU bottleneck is more exposed in strategy games, flight sims and Blizzard games.
R9 290 makes R9 290X irrelevant but I would wait for after-market versions only.
A stock i7 930 2.8ghz gets 85 fps average in BF4 at 1080P with Ares II but you need an HD7990 to hit that. That means you'll be GPU limited most of the time with an R9 290. If you overclock your CPU to 3.8-4.0ghz, you should be good to go for even 20nm GPUs.
http://gamegpu.ru/action-/-fps-/-tps/battlefield-4-test-gpu.html
I think you are going off the wrong assumption that i7 @ 3.4ghz is roughly equal to Phenom II 3.4-3.6ghz or 4.0ghz Bulldozer. This is incorrect as a 1st generation i7 2.8ghz is about as fast as a 4.0ghz FX8350 in CPU limited games that don't use more than 4 threads. But of course it is not possible to fully eliminate the CPU bottleneck as some games are bottlenecked by even a i7 4770. It just depends on the types of games you play.