We completed update 6 / sp 20 from update 2 / sp 16.1 a couple of months ago. With thorough testing and good retrofits documentation, you should be fine. There are some new bugs introduced in update 6 that you might want to be aware of - off the top of my head, dates on financial reports are incorrect - the fix for this is to a business function and is in update 7, and some code behind the P0472 is missing and will have to be re-added manually, again fixed in update 7. There were a few others, but I do not currently have access to our Issues Log where we recorded them. The update definitely fixed some of our issues, but several remain, to be fixed (we hope) in update 7.