I guess the question is, "Can we optimize our testing by using WinRunner and/or SilkTest?" The answer may be, "You can't." It may be that they're both the wrong tool. I'm assuming that you currently are not using WinRuner or SilkTest or any other canned automated testing tool. What are you doing right now to test your application? What kind of application is it?
I would not be so clear cut as Cypher, my answer will be "It depends".
What are you trying to optimize ?
If it is regression testing, I'd say that automation tools can help test faster than manual test.
If it is performance testing I'd say no, you should better use some dedicated tool (LoadRunner or SilkPerformer to stay with the same vendors)
If it is traceability, documentation, coverage, unit test, test case definition, test planning, test evaluation, defect management, ... the answer is NO.