Actually i did the test, it's of the skin default by MX10, bh1.6.5.
I used that because very clean and with few colors, the tests are identical with the zap, the channels change simultaneously in both boxes, but my opinion this is normal, in the zap, the OSD graphic not refreshed, changing only the labels and do not depend on the skin.
While opening the channel list may be that there is some fraction of a second in more or less, but without timing my eyes can not see it

maybe we have different decoders that have different performances, i used vu+ duo.
In the short test i did, The zap is flowing in the same way, the writing flow fast
In view of the channels, both show the full picture in less than 1 second, I can better measure

The green panel idem...
The Blue panel seems a small slower, maybe (maybe) because is present other additional pictures and use small clock that definitely takes away something
The menus are shown and move in the list in the same way
Basically
I knew that more details and more graphic (like big watches) would make the skin more heavily, but in comparison i did not see differences, rather they are surprised at this, then maybe i will be denied, but for me, makes little difference if a page is displayed in 0.8 seconds or 0.6 seconds, these differences were not significant and and few people realize it.
Certainly there is scope to improve the performance, i think of all the images that i dont have optimized because the gain in size (and loading time) are very very minimal, but it an exercise that you can try.
Finally a last remark, as in graphics or photography, more detail and more color means more weight, if i create a black window with white writing, this will faster loading of a window with more images, pixelated Background, chrome pics, edged and shades, by means that do not compete on speed, but the look of privilege.
I believe that in comparison with other skin, (especially with certain styles), there will never be the possibility that a skin like carbon can be faster than a skin like rihanna, styles and content are too different, not speech of beautiful/ugly, but i like more than what i like most style or the other
Thank you for reporting, I will continue to tests
bye