The cone's gonna be in the engine bay and doesn't use the stock airbox -> Higher intake temperatures -> which will rob a some of the 65 ponies you have under the bonnet. Heck, if noise is what you want get a free flowing exhaust. Then again, that reduces backpressure, which on a N/A car reduces performance. More noise...less performance, if that's what you want?
Panel filter using the stock airbox -> ~atmospheric intake temps w/slightly less restiction -> maybe 1-2 extra BHP
My advice? Do nothing or get a panel filter if you must.
And here's my my recent experience of an extreme case of lots of noise but feck all power - I managed to blow a hole in my intercooler to turbo hose on Saturday. Sounded like I had a HUGE turbo which was whooshing very loud indeed as I went up the revs. Whilst this would appeal to a certain audience, I felt rather embarrased with my car sounding like it had a dump valve. Not long after, then the boost pipe deteriorated even further and I lost all boost -> feck all power. Car was strugging to do 60 MPH uphill on the M1 -> not fun. VW assistance temporarily taped it up using amalgamating tape as it was past 12 PM, meaning VW parts dept was shut and I couldn't get a new hose. It's held up pretty well for the last 300 miles - managed to get me to London on Saturday and get me home today. Off to get a new pipe tomorrow.
Ash