A complete Shimano 105 groupset weighs about 500g more than a Dura-Ace groupset, and about 200g more than an Ultegra groupset. But when you buy an Ultegra bike or groupset over a 105, you usually end up paying hundreds of dollars for less than a pound(454g), usually around one dollar per gram of weight savings($1/g) or less. A Dura-Ace equipped bike has even worse returns on $/g. Cost of replacement for parts and consumables also increases for that marginal weight loss.
Instead of trading in your 105 bike for an Ultegra bike that’s only a bit lighter, it might be better to consider some upgrades. If you upgrade your bike later, you can still carry over the parts to your new bike.
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