high traffic on cf?

Yes, if you scale your code correctly, you should not have any problems.
We had 6-9k unique visitors the first week of every month a few years back using ColdFusion 4, then 4.5, IIS and SQL Server.
CF on one box, SQL on another. No problems with handling the load - at all. Response time was great. And each user would be online for at least 30 mins each. Heavy DB activity, inserts, deletes, updates, searches, etc. System still runs today using updated versions of same software. More servers and user though, and it flies!

Remember, if your apps are DB intensive, that will slow down your response time greatly.
IT WILL HAVE NOTHING TO DO WITH COLDFUSION.
Make sure queries are tight, tables normalized, Full-Text Indexing, Filegroups, etc, etc. Also, HD speed plays a BIG part.

I've read so many times where programmers blame CF for poor response time when the cause is bad programming, badly constructed DBs, cheap hardware, etc.

When tuned right, CF can really rip!

Yes, the code is everything ... bad code = crashing systems, regardless of technology used.

We run 2 sites on a single dual Xeon 2.4 1GB Ram Win2003 (IIS6) server + 1 SQL 2000 Server on Dual PIII 1.7 1 GB Ram Win2003 Server

Site A does approximately 1 TB of bandwidth per month ( nope, not a typo), and the second has about 30,000 visitors per day.

So long as your code is ok, and you do things like cache pages and queries that are unchanging, then your biggest bottleneck will likely be NIC capacity and pipe feeding the servers.

ColdFusion will only be as stable and scalable as the code you throw at it (.NET will be the same way). Throw crappy code at it, and it'll choke with 2 users.

IIS can easily handle 13k users/day. That's nothing. IIS, as a web server is actually pretty good. I don't care to much for it as an app server though.

To backup my statement, our intranet server (a CPQ Proliant DL380 dual P4/3.2GHz with 4GB of RAM, SmartArray 6400 w/256MB cache, and 15krpm disks running CF 7.0.1 enterprise with two clustered instances) earlier this week served 3.2 million hits with 9k unique visitors with an average 7a-5p CPU utilization of 15% on a -single- app server.

And, we maintained an average page response time of 0.22 seconds. If I can do that on one box, you certainly should be able to easily handle that load on the infrastructure you discussed in your orginial post - again, if your site is coded to scale. Our intranet server has to host many (currently around 70) different kinds of apps (all healthcare related) written by developers whos skills run the gammut of pretty good to super talented.

While 9k/unique users is no where near your predicted 40k, keep in mind our intranet has a very limited audience (of around 25,000 people). But those 9k users are banging on the applications very hard 24/7/365.

So, in a sentence, yes, ColdFusion can certainly handle your predicted loads if correctly scaled.

Just look at macromedia/adobe.com. They're doing exactly what you're talking about.

http://www.adobe.com/special/under_the_hood/report3/

Andy