A stack-to-reach ratio in the 1.38–1.45 range is an excellent match for the kind of riding you're describing. This is the sweet spot where you get a moderately aggressive position that's aerodynamic enough to be competitive, but not so low and stretched out that you're hurting after an hour or two.
Bikes in this range give you a race-oriented posture without going full aero. You'll be able to generate good power, stay low when you need to, and still feel comfortable on longer club rides or hilly road races. It's the geometry many experienced recreational riders and amateur racers gravitate toward because it balances speed with sustainability.
You'd only want to go lower (under 1.38) if you're a very flexible racer chasing maximum aerodynamic advantage, or higher (over 1.45) if long-distance comfort matters more than speed. For your mix of fast rides and racing, 1.38–1.45 hits the mark.