Suppose you go from a A719 rim (565 g), 28 mm tire (320 g if Gatorskin), standard tube (120 g), straight gauge spokes (call it 280 g for 36) to an Open Pro (435 g), 23 mm performance tire (220 g), light tube (70 g), butted spokes (call it 180 g for 32). Assuming the same hub and brass nipples all around, those changes will save about 380 g (0.83 lb), mostly on the outer circumference of the wheel. You will notice the lighter wheels accelerate faster and feel quicker. The 1.7 lb weight reduction will make a small difference on climbs. Going from a Gatorskin to a performance, racy tire will also give lower rolling resistance. The narrower tire is a bit more aerodynamic, another small difference at higher speeds.
These are each small - maybe very small - differences, but they add up to something that should be noticeable to most riders. Won't matter when you are fresh and/or just riding around. When you are tired and/or pushing hard, it will matter some.
Of course, getting stronger and lighter yourself will make far, far more difference. But that's not what you asked.
Open Pros are a good rim. Strong, reasonably durable, reasonably light, not too expensive, not very aero, available in various drillings (28, 32, 36). I have them on three bikes including my daily commuter. I've built those wheels and the Open Pros always build easily and true. I haven't experienced any quality problems.
That brings up something else. As long as you are doing this, consider having the wheels handbuilt. Find the local bike shop that does a good job with wheelbuilding. Handbuilt wheels are really nice - that is a whole other topic.
The one negative is, the Gatorskins are quite flat resistant and you'll give up some of that with a racy tire. Well, they make Gatorskins in 23 mm and 25 mm too and the folding bead versions are reasonably light.
Oh (edit), I guess you might find the ride harsher with 23 mm tires. Depends on what you like and what sort of roads you ride. I don't mind it myself. You will have to inflate them to higher pressure than what is necessary for 28 mm tires.
Last edited by jyl; 02-18-15 at 08:39 AM.