If storage and portability isn't an isssue. If it were me, would choose the larger one, is roomier, drags less. Bump that 8.0 into a 9.8 HP (carb swap) to plane faster the revitalized combo. A 8 footer is just a basic tender for very limited uses, definitely not ideal suited for the type of boating you are already doing or plan doing in near future with a more sea capable sib. You are starting very good, as both are high quality Hypalon made.
Agreed that a rib cuts water better, but on slight, medium choppy, windy, wavy seas conditions tubes will bump accordingly because small tenders are shallow deep keel versions. Literally will bang the whole bottom & tubes along.
Many boaters satanizes a sib performance due not topping air as factory stated, and even monitoring so with a gauge, not performing a reinflation during the day as temp cond changes so as water performance accordingly. Would go for a min 340 sib or rib any day, but that's me.
Anyway you shouldn't go at fast plane on those water conditions unless you have a solid built in kidneys & back spine too. As a courtesy to your passengers you must make their ride as comfy as possible as you would expect if being yourself a passenger sitting up front. As we all have experienced, the one who is driving is the least exposed to umcomfy bumpy rides.
If bothers you trading a top cond rib as yours for a less top cond sib, ask for $ 200-300 cash difference and buy a new 9.8 carb and a pressure gauge to top tubes and keel to its factory recommended working pressure for best combo water performance. I'm sure you will enjoy it much more than your current 8 footer, 8.0 HP combo.
Happy Boating