Modifying database file

All the database files are set to autogrowth to 10% from the initial sizes. But,the auto growth can happen any time during business hours causing the database slow down. Therefore I am taking the following approach -

1 I have set up a sql job ( calls a script listed here) that logs the current datafile and the log file size in a table in interval of 4 hours daily. I use that historical data to research when the data file needs to grow.
2. Then I run this script from the table to find which database file has more than 95% filled up and those are the candidate for me to manually resize ( expand) the data file.
3. I use the follwing script to resize the datafile
use db1
Go

---select * from sys.sysfiles

alter database client_343
modify file
(
name = client_343,
size = 1024MB
);