Just curious as to which of the leaks you used? Been using it for a few days now & it's fine.
I have been running the Nandroid backup of the second leak provided by Jack Barrett here: http://forum.xda-dev...d.php?t=1837455
He's basically done all the work for you, he started on the required stock rom & baseband, the applied the new OTA leak did a factory reset then a Backup.
All I did was copy his Nandroid backup into my relevant folder on my SD card then wiped everything & restored the backup, then wiped again.
I haven't had any of the issues you listed, re-downloaded all of my apps including paid ones fine, scrolling is fast, CPU usage doesn't seem any different, restored my old messages from a backup & new ones work fine & today I have been out in the car using the Sat Nav from 12:00 am - 9:00pm and it was spot on the whole time.
Strange though that there are a lot of reports on XDA that this or that won't work, but I think a lot of people are trying to OTA from the wrong base rom or modem etc. or they aren't wiping.( in general I mean, not pointing the finger at you )
The method in that thread I linked seems to be the most stable way. I saw Paul's tweet that he had installed on his S3 & thought it smooth too, might be worth while seeing what method he used or if it was something he built himself....
But for me as a daily driver it works fine, could do with a full rom to install from scratch though, update file is a bit of a cop out by sammy.