My first good Mars with the 140. Started with mono viewing and went up to 6mm. There was a 20+ deg C difference between inside and outside, and, as usual, the high mag image looked like crap during the first 30 minutes. After that, very, nice and further improving until about 45 minutes.
At 150x the 140 is too bright for the brighter planets. There was still a lot of glare, and I switched to binoviewing, which helped quite a bit. Since there seemed to be still more magnification possible, I inserted the 1.25 GPC, which helped a LOT. But the image still seemed too bright. Next I lost heart because a thin veil of clouds started moving in. But to my BIG surprise, the clouds cut out enough light (Mars still visible, but most stars gone) to show a beautiful, well defined pole and the features around the Sinus sabaeus started to show fairly detailed outlines. Oddly, the clouds also cut out (I swear) the atmospheric dispersion. Wow, I got so excited that I forgot everything about trying filters. That was a really good session.
I also tried a Vixen HR 2.4 which arrived last week. With the GPC it would be around 2mm and about 500x. Mars essentially lost its color and turned into an almost featureless grey disk passing rapidly trough the field of view. FOV/transit time were still tolerable (all manual mount), but the image was much worse than before. I will give the HR another chance when there are no clouds, but unless the difference is dramatic, it will have to go.
The GPC helped more than I expected for an aditional 1.25 mag factor. I think it's really the correction of the prisms effects that made the difference at high mags - maybe combined with the 140 doing better with mirrors than with prisms in the first place.