I ran some test with a HD jumpback file at random playing back from a MTRON SSD - Quad intel 2.66GHz
I rendered out photjpeg files at different compression rates.
then tried to playback 2 layers-
The Raw File played at 11fps
photojpeg 40% 55-60fps
photojpeg 50% 55-60fps
photojpeg 60% 55-60
photojpeg 70% 55-60fps
photojpeg 80% 35-40fps
The reason why you need to test different compression rates in photojpeg is that movies vary hugely in their compression value depending on the content.
And the overall data rate of the movie is more important than the compression value.
You want to make hidef work you have to do some tests.
No other codec comes close to photojpeg.