Thank you all for advice and comments. Much appreciate it.
A larger scope is at of question for the time being, and I'm quite happy at the moment with the short tube and performance of my small fast refractor on a manual alt-az.
I have TV 2x Barlow but feel that although it works nicely with my 13mm Nagler, for high resolution planetary observing (as high as one can expect from a 4" glass) I prefer to keep it simple and without a Barlow. Will think of Powermate though.
I did notice slightly more detail with 3.5mm Delos than with 5mm Delite, so perhaps a bit more magnification with a 3mm Delite might be the way to go for Mars, Saturn and the Moon, to test the waters, before I consider a 2.5mm TOE.
Thank you all again
