You were right, debug version is slow, release version is OK.
I believe you are using debug version of 5.2.3, which is naturally way slower than release version. See my today's email for link to release version of 5.2.3.
I am now using beta 5.2.3 build 3410 and since the first time I opened a document for editing I noticed it took more time to download and open than in 5.2.2 beta (build 3267).
As I keep the old exe too, I did some rough testing.
I started uploading/downloading the same file with both versions.
I get around 3 times slower transfer speed with 5.2.3 than in 5.2.2.
Protocol is SFTP.
I am moving back to 5.2.2 :cry: