A few things, you're limited on HP, you're limited on rigidity. At this point you aren't touching your HP limit. Most indexables, with honed edges on the insert, which you have, will take more HP to move metal, they can beat and bang pretty hard.
With the indexable you have, I would suggest going deep and narrow, instead of shallow and wide(where you can), you will be able to feed faster due to chip thinning (do a search), and use up more of your insert, instead of just the bottom corner.
Having experience trying to make money on floppy machines (your's is), solid carbide vari flute/helix endmills work very well. The trick is to twist the machine up in one direction and keep it that way, narrow and deep to get the head tweaked off to one side, or when slotting(cutting full width), ramp in slowly to tweak the head upwards. Keeps the chatter down and extends your tool life.