I haven't measured performance for this specific routine, but I have compared performance between CLR and COM calls in the past (i.e. for retrieving HTML from a remote server).

CLR is faster--and is the preferred approach suggested by Microsoft and most developers.

COM is simpler to deploy, and performs adequately for many things. With COM you can use pure T-SQL code, and don't need to register any assemblies on the server.

To illustrate the performance difference: a certain procedure using COM can execute 200 times in 22 seconds. The same procedure written using CLR can execute 200 times in 13 seconds.

So CLR is definitely faster and "better"...once it is written and deployed. Using COM is simpler to write and deploy if you prefer working in T-SQL and are not in the business of writing C# code and deploying .NET assemblies and CLR stored procedures.