Over which surface will the albedo changes due to clear and overcast skies have the greatest impact?
You should also consider that fresh snow atop the sea ice increases the albedo significantly. So the albedo for sea ice can fluctuate during a season. More clouds implies more precipitation, something we are seeing in a changing climate, so it’s fair to assume that changes in snow cover atop the sea ice will change as well. It may also make the change in seasonal albedo more dramatic, from sea ice to darker oceans. It depends on the weather patterns and the regions.
 Also, first-year sea ice will have a lower albedo than multi-year ice that has does not melt each season - though in the Arctic is type of ice is now very rare. 

If cloud cover increases over the oceans the albedo as seen from space will not change significantly, but again, the cloud types and heights will affect the albedo. But more cloud cover generally will trap more outgoing radiation enhancing the greenhouse effect. In a positive feedback loop. So, using you numbers, the albedo would increase, but the greenhouse effect would enhance, overall leading to a temperature increase. 

Land cover also varies, mid latitude regions are likely to see more cloud cover and more intense storms with climate change. An increase in cloud cover would again lead to changes in the greenhouse effect. With the albedo likely increasing (dark greens of forests, fields, etc having lower albedos etc). 

Overall your reasoning is sound, but it overlooks the effect cloud cover has on outgoing radiation from the Earth’s surface, more of which will be trapped and re-radiated by the extra water vapor.