Con
Glad to hear that the new scope is getting used. And very glad to hear that the folks at SASI are endorsing your decision.
The view of Saturn through the 16" I assume was at higher power? If so the image can often look worse even disregarding the height of it above the target as higher magnification can also magnify the atmospheric distortions.
Which lead me to my next point regarding eyepieces. My usual advice to beginners is stick to using the supplied eyepieces for a while. There are several reasons for this but the main ones are that it is very easy to spend a lot of money on eyepieces and not really get the benefit you thought.
The 26mm EP will probably be not a bad choice for a all round deep space EP. With the plossls, you may have heard that they are "crap", but go back a few years and plossls were pretty advanced EPs. They have a simple design so are inexpensive and their main issue is at short focal lengths the eye relief can get a bit tight. That said a 15 and 9mm should both be useable in your scope. By all means try a barlow, I am not a big fan myself but they have the advantage when used with a given eyepiece, the eye relief stays the same as what it is with that EP.
Just be very careful of interpreting highest useful manification. My 20" I think has a theoretical highest useful mag of something over 600x ( I have never really bothered working it out!
) but i have never pushed it beyond 317x, simply because the nights when going over 250x are so rare and really magnification is not really that helpful.
My first thing would be have a go using the 15mm (83X) and then the 9mm (139x) to observe Saturn and see what get the best detail. Try especially to see if you can crack Cassini's division in the rings or any of the faint banding on the planet itself. Then think about how cranking up the mag to say 208x (using a 6mm EP) would help.
Cheers
Malcolm