...or should I just choose quality 4 and be happy?
I always suggest to render as 16bit/TIFF, work it over in Photoshop and add a moderate "selective sharpener", import it into PTP and there set JPG to 7 or 8 max.
This gives you a moderate amount of data, speedy load and good quality.
Nevertheless the folder to put on your server will be around 150-300MB, depending on the amount of pixels, of course.
See two examples here: http://www.360impressions.de/Klap
(deep zoom on Android-Tabs also) done with a Canon 5D2 and 35mm Nikon prime. About 35000px width.http://www.360impressions.de/Medienhafen
(deep zoom on Android-Tabs also) done with a Canon 5D2 and 85mm Nikon prime.
About 87000px width.
In the meantime i use a D800 and D800E - the resolution is + 1.6 (have no example ready at this state which i can show - but it´s