If your pdfs are text only (apart from the cover image) they
might convert ok to epub or
may even be reflowable.
Also the Sony has fairly good pdf support in the new models including 2 and 3 column mode where it zooms to the column width of the first column. When you press the next page button or (touch the screen) it moves down to the next part of that column's text, press next page again and it goes to the next column.
Here's a review of the PRS-650 vs. Kindle 3
http://www.pcpro.co.uk/blogs/2010/09...y-handle-pdfs/
The best thing you can try is to put the pdfs on an SD memory card and bring it to a shop and try it in one of the display models(of the PRS-650 as PRS-350 doesn't have a memory card slot). It will give you good idea of how it will work on the PRS-350.