If you are targeting salmon/steelhead, I think a 253 might be a more versatile choice.
There is not much weight savings going to the smaller model and I use a 253 spooled with 150 yards of Power Pro 30 lbs braid line.
The braid is suppose to be same diameter as 8 lb mono, but a new 150 yard spool will fill to about 4mm from the rim, which is ideal for my use.
I have not filled it with mono, as I use braids mostly, but actual line capacity could be less than stated in the spec sheet.
Same thing happened with my Daiwa Tierra 3000 spinning reel which is rated at 240 yards of 8 pound test. I filled it with Power Pro 30 lbs (8 lbs dia) braid and could not spool the entire 150 yards and had to leave some off. If you are going to use 20 lbs braid, you could use the smaller reel, but thin braids are harder to work with especially when it is cold.
So do check around how much line the 103 and 203 actually holds, before you make your decision.