The low FPS drop could actually be down to your hardware not rendering the models quick enough. "Entities" are all the objects in the map, including player models and animations (like people moving, crouching, firing, dropping weapons, reloading etc). If the "entities" portion of your net_graph payload (the payload is the actual bar graph part of net_graph, with all the colours) is spiking, then this is most likely true.

There are several ways you can edit your game to minimise the amount of "entities" that are being rendered in the game at one time. You could turn off stuff like decals (bullet holes, scratch marks), turn off excess models (like trash), make ragdolls disappear when not being used (basically makes dead bodies disappear). There are many ways. I wrote a thread a while back on how to tweak your games graphics using autoexec. It's pretty simple, you just read through and decide what you want and what you don't want.

Other solutions would be more hardware related. Getting a new computer would be a benefit, or even just a new graphics card. A new ISP could be more beneficial, as you'll be able to send/receive packets quicker, meaning that your graphics card has more time to render the models (and therefore the events) quicker, meaning you're PC won't get these huge lag spikes where lots of things are trying to be rendered all at the same time.