Well I guess this is a good case for testing out myself. Once I have built out a test case and sample project I will build it and run it on my surface RT to test it in both modes...
There are only relatively subtle differences between the two environments and I would expect performance differences to be negligible. Some browsing of browser benchmarks that include IE10 (browser) and Windows 8 apps confirms this.
Actually, the IE10 performance is pretty great and the touch support is too. Check out ietestdrive.com and compare some of the demos there in various browsers.
Develop games in your browser. Powerful, performant & highly capable.
Thanks for the reply. I am definitely familiar with the perf of IE10, my main purpose was just checking if the Windows app had a any additional optimization for html5 apps. Without webGL or a Windows 8 implementation of appMobi's directCanvas to give some added performance I am trying to make sure the games perform well as Windows 8 apps and Windows phone apps without having to alter the experience too much.
I still have my fingers crossed that there will be a Windows based option that works in IE to bring game perf and framerates up to a similar level as the above mentioned technologies.