Last week I was having a heck of a time rendering an image. I would lower the bucketsize to 32 and reduce raytracing,  and still got the memory error.

Finally I went to my graphic program and located all of the textures for everything I used and reduced them in size using "bicubic resampling" to 1024 on the longest side.  I saw that some were 4000 pixels!  Resizing the textures helped immensely. I didn't have any closeups so I didn't need huge detail and 1024 was more than adequate for my needs.

I still had to reduce my bucketsize to 32 though but didn't have to sacrifice raytracing.

I made a copy of the original textures in case I ever want to use them at full size.

Also, check the shadow map size of your lights.  I had trouble once and eventually found that I had one shadow map that was 8000 which was what was hanging up my render and causing memory issues.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi