Experiment with all of the frame improvement configs: dx8 high frames, dx8 max frames, dx9 high frames, etc. Different ones perform differently on different setups, so the best way to see which works best is by testing each of them.
There are reduced particles you can use that remove projectile trails, most smoke and explosions, and significantly reduce the amount of visuals going on. Though this won't work in matches with sv_pure, it should give you a noticeable frame boost in all other environments.
No-hats mod is also an essential for frame boosting, and isn't effected by sv_pure.
Also /experiment/ with different resolutions, not everyone's rig will handle things the same. For instance, I get the best frames @ 1280 x 720, compared to my native resolution (1440 x 900) and even lower resolutions (640 x 360). See what works best for you.
Keeping steam's use of your resources down to a minimum is important too, being this is the only other program you /have/ to have running while playing. Disabling notifications has removed a lot of frame stutters and freezes when they popup for me, as well as the in-game steam community.
Understand the rhythm of your PC, and when it performs best. For instance, I've gotten in the habit of restarting my machine, waiting 10 minutes to launch steam, watching my cpu temperature and usually turning on some additional fans in my room to lower the ambient temp, launching tf2 once I'm at my cpu's comfortable idle temperature, then grabbing an icepack and applying it about 1 minute into the program running. It took me a while to determine one of my main issues was overheating, killing my performance. Especially for those living in scorching, summery climate, it can be very difficult to keep the temperature of your room down to a level that doesn't also give your rig a heart attack. Watch your cpu's temp in relation to your pc, I feel insufficient cooling is a frequent issue, especially for laptop users.
If you do a lot of tweaking and spend time to see what combination of changes works best, you should definitely be able to get 60 fps, atleast /sometimes/. 35-50 isn't a bad starting point. Best of luck.