Hello:

Do you have the multi-core rendering option in advanced graphics settings in Team Fortress 2? You have to activate it. I mention it because I play with the signature team at 1440p (2560*1440) and on 32-player servers, and with everything on high or very high, without filters, the game runs well with the signature team. It may have some dips at times of nearby explosions or things like that but it is perfectly playable. And my resolution requires much more power than Full HD. I also don't know if you play it with many filters in which case it is normal that it can lag.

On the other hand, it is not the best micro for OC as they tell you, but man it is not such a bad team, don't worry.