Hi Stephan,
As John has just mentioned i have just taken delivery of SDM #68 a 28" f3.3 with a Mike lockwood mirror which is what you will be getting.
I have a26 nagler, 17 ethos ,13 ethos ,10 ethos at the moment , at coona the seeing was average on 2 to 3 nights & good on another few nights i had my 10mm in & that was about the limit that night which is i think around 380 x i'm sure with good seeing that my scope will be able to handle much higher mags.
But most of the time i was using my 17 mm or 13mm . i will buy a 21 ethos next as i used one & it was great. As john said i'd wait & see before buying,
I would consider ethos i know they are expensive but with there wide view they gave me truly biblical views through the 28, i think they are worth it
phil