Carrera are measured differently - I believe the seat tube rather than the cross tube (google for the geometry specs), so you can't compare directly to say a Specialized cm measurement (as they use the TT I think). It might be more like a 58cm, so not surprised it's too big. Try a shorter stem again, adjust the saddle position, flip the stem, turn the hoods towards you. But it may never fit right if the frame really is too big (probably closer to an XL Sirrus)
What she said, i have had a few carrera road bikes , serial
halfords c2w user and they measure the seat tube to where the top tube meets it . as all the road bikes have sloping top tube this give a false measurement when compared to the old standard of measuring to a level top tube or "virtual " top tube to give frame size.
My old virtuoso was sticker-ed 19 " which is a 48 but it was more like a 53 , the way i size bikes now is to measure the top tube ctr to ctr to let me know the reach .
My 2 road bikes have both got the same reach although one is a bigger size so i use an 80 mm stem to give me the same set up , i used to get aching triceps as well if i used too longer stem.Assuming you have your saddle height and set back right a rough rule of thumb for reach is look at front wheel hub and it should be hidden by the handlebar where it clamps into the stem .
saddle drop or how much lower your bars are is up to you, dont worry that your handle bars are lower than the saddle if your comfortable, if not then flip the stem or you can get riser stems that raise the cockpit .I am 5 foot 7 " and i have about 5 cm of saddle to bar drop and i think taller people can have more ( i think longer arms = more drop ) but they might have the same body angle .
You might also be getting used to a road bike set up, when i first started i used to have the bars level with the saddle but as my core got stronger and i got used to riding i have gradually got lower .
have a look at ........
http://www.jimlangley.net/crank/bikefit.html
http://www.jimlangley.net/crank/bikefitchart.html
http://bikedynamics.co.uk/guidelines.htm