You have to save every record (means the record of EVERY player in an array). then you can get the "longes" jump with something like this:
PHP Code:
new max = get_maxplayers()
new Float:longest = g_record[1]
for(new i=2; i<=max;i++){
if(g_record[i] > longest) longest = g_record[i]
}
now in "longest" the longest jump is stored