Weight: what the grams mean
The Rapide CLX III is 250 g lighter per pair (1,305 g vs 1,555 g, manufacturer claims).
On a steady climb only total weight counts: a gram in the wheels costs the same as a gram in the frame or a bottle.1 A common rule of thumb is about 2 seconds per 100 metres of climbing for every kilogram, so 150 g works out at roughly 3 seconds on a 1,000 m climb.2
Rim weight matters somewhat more when you accelerate, because the rim spins as well as moves forward; physically that effect is at most about twice that of frame weight, and only while speeding up.1 Claimed weights are measured differently from brand to brand: some include rim tape and valves, others do not, and tolerances of around ±30 g are common.3 Independent weighing usually lands close to the claim once tape and valves are accounted for.4