Of course the amount of clouds/sun can have an impact too but I'm sure you are probably familiar with that aspect of things fishing for trout.
Sure ! in my local stream, I fish most of the time with dry flies. There are differents hatches depend of the sun light. With little rain and cloudy days, we have a lot of mayflies With the sun, caddis flies, on the end of the day
For egg flies, I mostkly tie with regular glo bug yarn. But, I wasn't familiar with tying these flies, and put a lot of materials (for sucker spawn). Now, I know that less material is better for realistic, and translucents fly, with "dot".
About size, I see on the web, that size 10 and 12 are basic sizes for the Salmon river
I will send more pictures of my flies, let see what do you think off !