higher peak rpm needs shorter intake, lower needs longer (hence the 2.0TS gets the variable intake manifold).
for example, the alfa 16v TS has a pretty lame 235 degree intake cam...
take this intake cam paired to 45mm runners, to get optimum torque at 3000rpm the optimal intake length is aprox 70cm (valve to filter), to get the optimal figures for 6500rpm the intake is shortened to aprox 20cm. you will never get it this short
The alfas have the variable intake manifold which can control the runner length some what to give improved torque low end with plenty power top end, best of both worlds. however you can still change the torque curve slightly by changing the length of the intake. just remember, shorter intake = higher rpm range. What you should think about doing is finding the optimum length from valve to filter to give a balance of both low and high rpm usage, unless you only use high rpm then by all means shorten away
Manufacturers are normally pretty close to spot on with the intake lengths tho and the pipe between TB and MAF is pretty well made, smooth bend so IMO not worth changing, unless your just wanting to make the engine bay look nicer
This said, these numbers would suggest the intake could be made slightly shorter. Can anyone confirm the intake runner diameter and I can calculate the exact lengths for given RPM for you.
I hope your still awake