In my experience, 1/4" 2 flute tools will speed things up on certain materials such as HDPE, which is self-lubricating and stays cool. If your CAM software supports it (I.E. Fusion360) it helps to use helical or ramping entries and reduced corner feeds in your tool paths. They reduces the impact on the spindle, which on the Nomad tends to stall.
Speed is kind of relative in my opinion. Noise is my bigger concern. Lately I've been using smaller stub length cutters and just letting the machine run fairly quietly and conservatively for longer stretches. However, if you are new, expect to break a lot of cutters in the beginning if going this route. 1/4" cutters are much more robust. Either way I would strongly suggest using coated cutters, especially if not using some kind of coolant or air.