populate form data based on dropdownlist selection

Hi Guys

i am looking to the best way to get my form data populating based on DDl selection. i am loading data into Javascript arrays and populate which becomes slow with number of records..

Any fastest solution ?

iam using CF MX7 and we;re may be planning to move to CF 9 but do not know Wehen ?

iam looking for now msolution

thoughts ?

thanks