The middle cogs on my DA 12/27 cassette are showing some wear, as evidenced by some slipping and/or, a bit of delay on up shifts with these particular gears. The wear is not surprising since I spend most of the time in and around these cogs due to the terrain. It has about 2.5K miles on it, give or take. Since these central cogs are steel, whereas the other cogs on this set are Titanium, can I buy an Ultegra 10 speed cassette (12/27) and just swap the central cogs over to my DA cassette? Its less expensive this route. Or, do I need to buy another DA cassette?