You did a great job on the Tempo. Personally, I wouldn’t be too anxious to start mixing up the components on it. Maybe a full trade up to tri color or Dura Ace 7400 if anything.
Until then, 28 teeth on the back will make a big difference. I’ll assume the cranks are 130 BCD in which case I’d also put a 39 on the front. Doing both might get you by without changing chain links. 39/28 will be the limit with a short cage derailleur and standard crank BCD.