Mike and Aylin:
Thanks for the suggestion Mike. I did what you suggested and added my spreadsheet into your test program. The results that I see from that test are different, in that the SetValue() time does not get slower as it goes, but it seems slow from the start. The time to do 1,000 iterations of SetValue is about 12 seconds, while the time to do 1,000 iterations of GetValue is about 20 milliseconds.
In my real program, I am building the spreadsheet dynamically, so it does get continuously slower as it gets bigger. On my larger spreadsheets, it gets painfully slow, about 10 minutes.
I realize that the SetValue function may be slower, but it is 600 times slower than GetValue, and the speed is related to the size of the spreadsheet, so hopefully this can be fixed. I am going to upload the modified test program in a ticket, in case it can be used for testing by Telerik.
I have attached a screenshot of my test results.