Hello, TS, and welcome to GTPlanet. If you check out the Read This: threads, and try a search of this board, you'll see a lot of existing threads on 'top speed'. Enjoy your stay.
with out the wheelie trick 539kph is good, i think i got around 550 without wheelie trick. oh and if you dont know what the wheelie trick is then do a search.
basically lower all your suspension settings, full downforce on rear and none on the front get the escudo to about 370ish kph as quick as you can and it should do a wheelie.