I welcome people making actual suggestions on areas where Ext can be optimized, but I grow very tired of hearing people complaining about performance (like that one guy who wouldn't give up the mic at SenchaCon). I have built very large applications on multiple versions of Ext and I have not had any significant performance issues, even with 4.x. If a developer finds himself in a state where he can not overcome some issue with performance (or any other part of Ext for that matter) he should:
1. Be specific and try to identify the problem area
2. See if any workarounds exist
3. Seek out help from either forums/Sencha support/ or a third party consultant
4. Stop pretending 4.x is incredibly slow. Many people have written large 4.x apps.
4.x is miles ahead of 3.x. I enjoy working with it and find the improvements well worth the unnoticeable performance cost. And while I have seen some noticeably slow Ext code in the past, it has always been fixable and usually not directly caused by the framework, but by a developer blaming the framework. And if you do see something specific that is slow in Ext (in a realistic context - I don't care how many millions of times you can run something in a loop to show it is slow) you can work around it, or better yet, take advantage of the open source nature and provide suggestions/overrides to Sencha and the community.