Right about 50 the skill-ups slow way down. It's not the target that's causing the problem, it's just the decreased rate in skill-ups.
Synthing gold ingots can almost be a break-even synth, which you can do until 54. As you get closer to 54, the skill-ups will slow more. However, this leveling of goldsmithing starts to get expensive, and I always preferred slower skill-ups while maintaining a bank rather than burning through 10k per synth on things like gold chains.
Once you're past gold ingots, you'll have to target some gold rings, earrings, and hairpins for a while. They all average about a 10k loss on Asura, so pick your poison. It'll ease up a little when you can start targeting Platinum Ingots (61), which actually synth for profit on Asura.
The real question I have is where are you taking goldsmithing? Are you just capping it at 60? If so, you really have to decide if there's a target synth out there that makes this move worth it. If you're taking it to 100, welcome to goldsmithing hell and enjoy the pain.