Here's a set of benchmarks comparing your 1090T to a modern i5:
http://www.anandtech.com/bench/product/1544?vs=146
If you scroll down to the gaming benchmarks and look at the R9 290X and GTX 980 results - which roughly comparable to the RX 480, there is clear evidence of CPU bottlenecks in some games, Grid Autosport and Total War are good examples. GTA V has some bottlecking too. There's only a few games in the list so it's hardly conclusive, but it's pretty solid evidence that your 1090T would be holding back a 480X in a good number of games at least.