You are correct with DDE. However, we were looking at 1800 symbols using a couple 3rd party apps (QuoteIN and XLQ) which run off IQFeed and utilize RTD to feed Excel instead of DDE.
Running 1800 symbols is obviously a strain with the amount of data being processed (by IQFeed, 3rd party app and Excel each needing to touch/process it). In our tests, a P4 2.0 Ghz machine with 768MB ram just couldn't handle it. 100% CPU utilization. It is very likely that part of the problem was memory swapping, but in any case, it just wouldn't work with either XLQ or QuoteIN.
On the other hand, we tested with a Core 2 Duo Processor with 2GB Ram and were able to feed 1800 symbols using both XLQ and QuoteIN effectively. In both cases, the system consistently had 50% CPU idle (IQFeed taking up less than 10% CPU). For many, using 50% CPU on a high powered machine isn't going to work, especially if you need the machine to do other tasks. Unfortunatley, with the combination of IQFeed, 3rd party app and Excel, it just takes some horespower. In all of our tests, Excel was the biggest utilizer of both CPU and memory (consuming over 100MB of memory).
Hope the background and test results help for anyone curious...
Jay Froscheiser
DTN