Going from final spin speed of 800 to 1400 or even 1600 gives biggest bang for buck in terms of less residual moisture. But even then that would vary by type of textile (thick and thirsty bath towels/wash cloths, heavy cotton blankets, and other such things), and construction.
Anything above 1400 you're getting into such small percentages of moisture extracted that energy use in tumble drying isn't that greatly reduced. This compared to the stress and strain on washer I suppose.
Keep in mind washing machines have much larger drums than spin driers.Thus even though final spin speed might lower than the 2800 rpms of spinner, more water is extracted in a given time thanks to that larger drum.
Many front loaders use early portion of spin cycle to periodically to stop, fluffing up washing, then spin, stop...... This helps extract more water from items because process is more evenly done.
In a spin dryer things are mashed down and spun as loaded. This can create pockets or other areas where water doesn't extract evenly. You notice this when taking out washing somethings have nearly dry streaks, whilst others are moist or even wet.