ExtJS 4 - Real time issues

1. For large datasets there are too handle it, infinite grid and buffered rendering grid. 
The main difference is the infinite grid sends requests to load data on the fly where buffered rendering grid retrieves all the data in one go and the grid will only display a portion of that dataset based on the size of the grid. 

http://docs.sencha.com/extjs/4.2.1/#!/example/grid/infinite-scroll.html 
http://docs.sencha.com/extjs/4.2.1/#!/example/grid/buffer-grid.html 

If the slowdown is the store loading all that data then I would suggest going with an infinite grid. If the slowdown is the grid rendering all that data then I would go with the buffered grid.

2. 
You can use extraParams to send any extra data in an ajax, or just before you issue the update like so: 

var cfg = { 
myprop1: 'myvalue1', 
myprop2: 'myvalue2' 
}; 

store.getProxy().extraParams = { 
props: Ext.encode(cfg) 
}; 
record.set(values);