id have to say mate, if you can hold out, do it, wait for the cash. i just brought my second lex, same spec as yours, with 12 months tax, nov mot, already modded tastefully and in mint condition for 3400.
its a buyers market, you could get so much car for 4250. On auto trader there is a silver sport navigator, 54 plate, 63k, cam belt changed, looks brand new, he wants 5k for it, i got him down to 4200! i was so close but then had a moment of sense and realised i should really save the cash as i have a baby due in 7 weeks!
seriously mate, wait for the cash and you will get a 5k car for the 4250 you have got, either that or your gonna buy a 3k car for 4250 from a a garage.
just my opinion :)