Multi Axis Slow Feedrate

Hi everyone. I know this topic has been covered before, but I would like a bit of advice specific to my machine as I'm not that well versed in LinuxCNC.

I've built a 5 axis rotating nutating (head-head) type CNC and it's been running well for the past 1.5-2 years. However, I'm getting quite slow feedrates on certain multi axis operations and it's becoming increasingly frustrating.

As an example, this image shows a test file where the X and Y axes barely move, the Z and A axes don't move, and it basically just rotates the C axis. At a specified feedrate of 4000mm/min, it's only cutting at about 600mm/min. My max velocity for linear axes is 25,000mm/min, and angular is 4500deg/min. Acceleration is relatively high, and 4000mm/min should be achievable.

 

I'm using Fusion for the CAM, and the above test file is using swarf machining. This can only be output as a bunch of small lines, so I've gone as coarse as possible with the tolerance and that's set at 0.1mm, and I'm using P0.1 Q0.1 for smoothing. And I'm using TCP.

Correct me if I'm wrong, but is the slowdown in the feedrate due to the 1 line lookahead in multi axis?

I have a separate LinuxCNC config setup to run my machine as a simulation, and it uses a different ini file to my machines so I can test files prior to running them. With this ini file I've bumped up the max velocity a bit, and really bumped up the acceleration, and I've been able to get the required 4000mm/min. However, these velocity and acceleration speeds are very unrealistic for my physical machine.

So my question is, is this just how LinuxCNC is? Or am I doing something wrong? Or is there a workaround for this issue? I've also tried using inverse time, but it gives me the same outcome as programmed feedrate. Let me know if there are any files I should post (ini, etc). Thanks.

Here's a couple of photos of my machine.