Okay, more seriously (I've been cogitating):
Every centimeter (maybe even every 5mm) will make it a bit slower to tip your ski. It's more effort. But I say this as someone who at 5'5 has happily skied 113mm waists in all conditions from Colorado hardpack to two feet of snow. It's just an adjustment when you go from something narrower to something fatter, but once you're used to it, it's just the way the ski feels. At your height (and presumed leg length), I really can't imagine any width being *too* fat for you - just a matter of preference. But whenever I go up in width after skiing something narrower for a while, the first few runs on firm snow feel like I'm on planks. Then I adjust to the difference and it's my new "normal."
People will tell you that it is harder on your knees to ski a fat ski on *hard* snow. I never noticed until last season, rehabbing after ACL surgery. All of a sudden my beloved all-condition 113s were hard for me to tip. They were still just fine in powder, but suddenly I understood why people said they were harder on your knees on groomers. They really are. But it wasn't something that bothered me until all this mess. Still hoping it will sort itself out.
Is there a skill progression? Sort of. As I said, the fatter the ski is, the slower it is edge to edge. This means that unless you have good skills already, it's easier to get sloppy with fat skis. Fat skis are "cheaters" for soft snow, but they are the opposite on hard snow. For your stats, I'm not sure I'd even call a 108 fat.
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