The FPS spikes going up and down will be looked into, but there is always overhead when running the bot. However, unless it's making the bot flat out not work, that's not as big of a deal in terms of the bot being broken.
That is, I see those same drops myself when testing right now in dried lake, but it's not affecting anything. As long as it stays about 20 fps consistently, even if it has dips, that's 'ok' for now.
Don't worry about the FPS display as much as the Frame Time display. Huge frame time spikes, above say 33 might be an issue, but in general, it should be pretty low if VSync is off.
Lastly, a lot of act 4 areas are much larger, and some have a lot more objects that the bot has to read when running, so I don't think anything is quite wrong yet. When I first tested in Belly of the Beast, I had to change the object explorer plugin because of how many objects are now being shown in the client. That's not to say I'm not looking into it, but, the client itself is far from being in an optimized, stable state.