Interesting questions, WH.
In order to avoid confusion I would like to tease out different terms. Firstly try to avoid the word 'lacing' in this discussion. Lacing is found in Silver Laced etc which is a clear gold or silver feather with an edging of black, blue or white. The markings in your birds are better referred to as pencilling, ie. two or three black, blue or splash bands on each feather. Also I'd avoid crossing gold and silver birds. It then takes ages to get well marked birds.
Your mating predictions in terms of Blue Partridge X Blue Partridge are correct. You would expect 50% Blue Partridge, 25% Gold Partridge and 25% Splash Partridge. Because you want to improve the size of your birds the way forward depends on selecting the best breeders in this respect. Whether thats Blue Partridge X Blue Partridge or Blue Partridge X Gold Partridge is secondary as either mating gives 50% Blue Partridge. Maximising of size also depends on avoiding excessive inbreeding. Buying in an unrelated Partridge cock will improve vigour and therefore size. Inbreeding often results in size reduction.
I've never seen a Splash Partridge bird. How precisely the pigments are deposited in the growing feathers and therefore how contrasting the overall look is I don't know. Many of these novel colours are unpredictable. I have at the moment one female chick (5 weeks old) that is Blue Silver Crele - a colour combo that I have never seen before. (A combo of Silver Duckwing Welsummer, Blue Jersey Giant and Cuckoo Marans). In two years time I plan to use her and her Blue Silver Duckwing sisters to breed a whole batch of Blue Silver Crele birds to see just how varied this colour combo is. At present we do not know just how much variation can occur. Similarly with your birds. How precise or blurry the pencilling can be is a bit unknown at present.
This site currently blocks pictures so I can't show you.
Poultry, sanity in a mad world!
Sheep, insanity in a rational world!