In my desktop I get a significant difference depending on the size of the images, the size of the canvas, and the size of the browser window.
My PC configuration is:
Intel Core 2 Duo E8400 3.0 GHz
4 GB ram
Nvidia GeForce 9400 GT 512mb
Win 7 32 bits
I will try to prepare a benchmark to have quantitative data to analyze, but I already made individual tests that resulted in fps drops related to the factors that I stated above.
Regarding setting 'point sampling' and 'letterbox scale' it works well for pixelated graphics, but for digital painting or vectors the blurriness normally looks better for upscaling than the blocky look. Then a sharpen filter can enhance the acutance in machines that support it.
Probably there will be a small drop in performance for every effect that you use. I used this trick in CC and I normally got good results.