if your engine is still nice, keep it stock is better..
unless your engine start to give way.. or you want more power then
SVT or BT will be fine, each will depend on your budget
afaik, BT 5 speed cost 5.5k (including h/cut + covnert labour, NOT INCLUDE JPJ/PUSPAKOM), and recently been to chopshop, discovered that a BT 6 speed h/cut cost Rm7k...price is going up.