First of all W3 total cache is amazing!
We run a small site with about 4m page views per month on IIS7. It has a gallery with over 2gigs of images that are now all being pulled from amazon thanks to W3TC. We never had any load issues whats so ever(well at least with hyper cache and wincahce enabled)but with 10 images per page at about 900x900+ pixels, CDN is obviously of great performance benefit! Server load is tad higher with W3TC but this is only because pages are being loaded faster. Amazon CDN makes image downloads so much faster its really amazing. So yes more clicks-per-second as a result, rather than waiting for images to load.
However, on IIS wincache is a lot faster than xcache, apc etc and it eliminates the need of memcached since it does that and more.
If you followed the instructions here to boost wordpress with wincache:
...then note that W3TC replaces object-cache.php located at the /wp-content/ on install which breaks one of the 5 types of caches that wincache handles... titled as "user cache".
To fix you'll here to replace the object-cache.php located in the /wp-content/ folder with the wincached version you installed before.
Note: that you can't use the opcode feature in W3TC once replaced. So this is not for windows admin who use xcache etc. Only affects wincache.
Another note, I tried testing with xcache (i keep it installed just a matter of php.ini changes) and enabled everything in W3TC to route to xcache but wincache is still a lot faster and "load" is a LOT less... a LOT.
I hope to see wincache support soon!
Hope this helps an IIS wincache admin who tries W3TC.