So can you already work there permanently, or do you have a grad visa? The grad visa sounds like a great opportunity, especially if there's a way that you can then find permanent employment there and stay beyond 14 months.
I can't speak for Ireland but salaries in the UK are shocking. If you're working in software development then as a fresh graduate you'd basically be guaranteed to be making double your UK salary in the US. I think you could easily be making 4 times what a UK graduate outside of London would be making within your first year. Living costs will obviously be higher in San Francisco but it's almost certainly worth it given how high the potential salary is.
I'm guessing you're still quite young, so the money you earn now has the highest potential exposure to compound interest. In other words this is the most important money you'll ever earn. If you're not entrepreneurial, not studying law, and not studying medicine, then this is probably your best opportunity to ever become rich.