I’m not sure it matters too much about speed of download for a casino homepage. Visitors expect a longer than average download time for these things. It’s more a matter of targeting your design to the type of players you want to attract. I don’t think any of the casinos you mentioned do that at all.
Just by looking at GoldenRiviera and comparing it to VegasUSA or RoxyPalace.com, could you really give me a reason to play at one in preference to the other ? They all look interchangeable. There’s nothing to separate any of them in what is an increasingly crowded marketplace. I think you need a design that focuses strongly on whatever your USP is and is themed around that. Something that stands out from the crowd and definitely doesn’t look like other online casinos.