Gold on monza is very easy (if you wana skip the chicanes) the trickiest corner i had was one of the right handers after the second chicane, 3 tries golded me monza, nurburgring was alot trickier i had to watch some video's on that then 30 mins later hit gold, half an hour into suzuka now and im 2 secs off gold, the trick is just staying on not being quick enough. I have tried this challenge on ds3, g27 and thruxmaster and ds3 is very hard, g27 (is just stupid in gt5 generally the FFB is just a joke, which is a shame since it cost £400) something like and thruxmaster or DFGT will make the challenges easier. Also watch some video's they will show you what lines you need, they have helped me so far.
EDIT: i find TCS off, ABS 1, SRF on everything else off (and Automatic) makes the challenge easier too.