This was my solution for 466 using 3,4,5,15,18,20. However, it could be done in 4 calculations (one step of which was 18 x 27, which is unlikely to be typically spotted by a human)
20 + 5 = 25
25 × 18 = 450
15 + 4 = 19
19 − 3 = 16
16 + 450 = 466
20 + 5 = 25
25 × 18 = 450
15 + 4 = 19
19 − 3 = 16
16 + 450 = 466