It will definitely not bottleneck the 1080p monitor, but you're not getting the cards' full potential if you game on a 1366x786 monitor. You can obviously put all the settings on ultra in basically every game with it but it won't look that great.
If you have a 1080p monitor then use the GTX 980 on that as it will still manage to get high/ultra settings in most games.
Hope I helped 😉