Folks, just want to give you an update here on what was causing the lags that were the original subject of this thread and how they've been overcome.
With the help of DTN and Linn Software, I have been able to resolve the problems I was experiencing. As it turned out, I was mistaken about the number of symbols being monitored in real-time by Investor/RT (I/RT). I have 550 symbols setup in my I/RT system. While I thought only 23 of them were being monitored in real-time, all 550 of them were, in fact, being watched on a tick by tick basis. This in turn resulted from one of the advanced data management techniques I have developed in I/RT not working as expected, specifically the one I use to control the number of symbols I monitor in real-time. Bill Linn, one of I/RT's principal developers, has carefully examined this particular technique and recommended a minor modification to it to ensure that moving forward it will work as expected. Naturally, I have implemented his recommendation and, having done so, do not anticipate there being any further issues in this regard.
I should point out that it is very easy, both in I/RT and in IQFeed (the DTN utility that actually receives their data on my system), to determine how many symbols one is monitoring in real-time. In fact, it can be done, in either case, in a matter of seconds. Because I was confident that the data technique I employed in this case had set the number of symbols to monitor in real-time to the desired 23, I did not think to check how many I was, in fact, actually monitoring. Had I done so, I would have seen that I/RT and/or IQFeed were monitoring 550 symbols instead. Interestingly, during the non-peak times of the trading day, I/RT was able to track all 550 symbols while maintaining lag within entirely normal bounds. However, when trading volumes picked up dramatically in the last hour of trading, it was not possible for the system to keep up with the substantially greater tick rates, resulting in the extraordinary lags I reported.
I also want to point out that had I checked and seen that 550 symbols were being monitored in real-time, I could, in a matter of moments, have adjusted that number down to any level I desired because I/RT makes it very easy to change how many symbols one is monitoring in real-time. It's really a matter of a couple of mouse-clicks and it's done. Well, there you have it. Naturally, I welcome any further thoughtful comments or questions from persons with an interest in this matter.