I've had the same problems of typing stutter, plus difficulty in pasting in graphics to notes, and indeed lost content despite synching. The problems have been around for a while, but the latest version I've been running is 6.11.2, windows 7, 64 bit, with an SSD (my work PC). The problems are worst in larger notes (e.g. 80 MBytes).
I know my home computer (3 years older machine and windows 7) has none of these problems when I run Evernote 6.2.4 with the same notes. So after trying everything I could on my work PC (turning off virus protection, frequent synching, rebuild the databases etc), I did a completer removal of Evernote 6.11.2, and a clean install of Evernote 6.2.3 (from: https://evernote.en.uptodown.com/windows/old).
So far everything is running smoothly, and all the problems I was having have disappeared. I have not checked what functionality the older version might be missing (in terms of features), but I am staying with it !
Hope that is helpful.