Garvan, Being as high spine to edge at the blade tip & of very similar blade shape as the santoku to its immediate left, I'd be inclined to call that 5th knife a santoku with a K-tip (kiritsuke tip).
My usual duo du jour for kitchen knives is an 8" Japanese gyuto style knife and a paring knife, either Victorinox or Murray Carter or 4" Henckles, at which length I think of it as a petty.
But the job at hand has a majority influence on what is the tool of choice to accomplish the job. Gouging out cores from halved apples/pears and splitting a watermelon/butternut squash lengthwise, or breaking down large cryovac'ed animal parts, obviously call for very different tools. I feel very lucky to live in a place & time where we have such a plethora of choices for those tools, both commercial and custom made.