Both can perform well. An insulated CAI can provide air just as cold, if not colder than a FWI, but not insulated the FWI is gonna do better every time. The only advantage I can see with having the CAI over the fenderwell is it isn't as restrictive. The FWI is going to have bends in it and its quite long, the CAI doesn't have to have any bends and it and can be very short. Also, the FWI gets dirtier a lot quicker because it is pretty close to the ground and it collects a lot of road debris compared to the CAI.
Zooomer used to have a FWI on his GTP and swore by it for a long time. He ran extremely well with it, and I'm sure he will tell you its a great setup. However, now he runs the Wizair box and swares by that. It flows better, and he has basically ambient temps. Did it make a huge difference? Of course not, but it might have helped some. Both are good choices.
Honestly, my personal preference is the CAI, IMO its the cleanest setup. But if you're trying to save a few dollars the FWI is a very good option.
1990 Maroon Grand Prix STE McLaren 3.1 Intercooled Turbo, 14.695 @ 94.49 on 12psi before cam/heads/etc.
1990 Bright Red Grand Prix McLaren 3.1 Intercooled Turbo, 14.819 @ 92.72, 189whp
1999 Grand Prix GT 9.75:1|K&N|160 tstat|No Ubend/Cat/Res|UD Pulleys|Ported M90/TB/Heads|XPZ|2.55"|Pacesetters|Stage 2 I/C. 12.442 @ 112.78
2000 Blue Bonneville SSEi Supercharged Gutted Airbox|K&N|3.4"|1.9'*|WP Pulley|Custom DHP|180*stat|41932'*|No Cat. 14.681 @ 94.80
2002 Dark Cherry Grand Prix GTP Supercharged & Intercooled
12.084 @ 114.38 w/1.743 60', 315.6whp, Fastest Stock Cam M90 GTP!
NOW XP CAMMED, 340.6whp with XP, stock heads, Gen 3 M90, 11.984 @ 115.84 w/1.750 60'!
Most HP Stock Heads Gen 3 M90 GTP!
2004 Red Monte SS Supercharged K&N|3.4 Pulley|1.9'*|180*stat|41919 plugs|3" dp|No cat/ubend|DHP|Shift Kit. 14.2 @ 98
GOT BOOST??? Friends dont let friends drive stock!