I have the Orion Janissaries and the Zvedza Stetlets, they are both excellent. I was surprised that you have not mentioned the Orion Polish Winged Hussars that are another good set. Also don't forget that the Poles had many foreign mercenaries so that the Revell Thirty Years War and A Call To Arms English Civil War figures should not be overlooked. As for cossack cavalry at present I use the Hat Napoleonic cossacks.
Hopefully, Orion will get around to releasing some Turkish Cavalry and Stretlets also had Early Russian Infantry in their future releases.