The general rule is that the lighter your bike, the easier it will overcome rolling resistance (we all know this). So using components that are light-weight is obviously better. The problem is that YOU still need to propel the bike. No matter how light it is, if the engine (AND THAT'S YOU) is not adequately trained and conditioned, that feather-weight bike is going no-where fast.
Nicholas, there is almost no way that you will be able to measure any gains comparing bikes that have ± 100 grams weight difference between them. You buy yourself wheels that weigh 100 grams lighter, and then throw two Energy Bars into the back of your jersey that weigh 45 grams each? Get my point? If there is a 1 or 2 kg gain, that's a different story!
Train your body to overcome the weight of your current equipment. If you are a sprinter, train with a rucksack and half a brick inside it! Your'e legs will get used to the weight. Next time you sprint for the line in a race, you will weigh half a brick less!
If you are a climber, train those hills with a whole brick extra! When you start that climb during the race, your legs will automatically be prepared for a kilogram of extra weight, thats not there!
Don't let technical issues such as lighter wheels cloud your vision. Remember what Lance Armstrong says: it's not about the bike.