Taking into consideration most queries rely on cluster index on client+date - as I can see it partitioning by date will certainly hurt performance during querying.
As a result of partitioning by date column SQL Server will build as many client+date cluster indexes trees as date partitions are created. You can check this by checking sys.partitions system table - you will find one client-date entry per date partition.
In this case I think you have to decide what is more important to you, a partitioning schema that helps during maintenance or a partitioning schema that helps during querying.
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Pablo (Paul) Berzukov
Author of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.