firstly try chaosgroup forums, also look at vrayinfo site. I have had light spots from time to time. I thinks its over bright bitmaps in your scene, check the info when rendering.
as for your setings. you can start to find the problem areas by weeding out whether its reflections that take along time, or whether you have lots of lights and so on. Vray is slow with loads of lights. Also when you do Gi it takes into account reflective surfaces. Try not to have any GI settings over 1.0, colour mapping slows things down, use your QMC sampler to reduce times, also limit the reflection bounces.
Bucket sizes, i have mine at 128x128, but its a dual zeon so it handles it. Increasing bucket size allows more of the scene to load and unload, but if your machine is slow then 64x64 is ok. Vray always take a while to clear the buckets if you stop rendering.
have you tried photon mapping? its great, very quick and its not view dependant.
I suggest posting you file or sending it to me, I will take a look if you cant get those times down.