As George has mentioned, the s54 M3 engine makes for a better base when running forced induction applications...
Cast iron block (yes, 335i has one as well) with forged internals, but more importantly, it's got additional capacity and revability, which makes it more suited to high HP turbo applications, as it can drive a larger turbo, and give you a wider & more useable power band. Considering that power is a product of torque x revs, the higher rev ceiling also automatically means more power at the same kind of boost levels, meaning a big turbo S54 will ultimately be the more powerful conversion.
If it weren't for the cost and intricacies of the engine's management and VANOS, I'd actually go as far as saying the S54 makes for a better base turbo 6-cylinder engine for a high horsepower turbo conversion than just about anything out there. Skyline GTR VR38 and Supra 2JZ included...
Fitting forced induction to a CSL - yes, that's sacrilege - but as far as a normal M3 goes, I'd say it's about as good as it gets for an aftermarket turbo conversion. The motor can make stupid amounts of power with relatively little work, and the rest of the car has the correct underpinnings to put down & use that power more effectively in stock trim than a 335i.
Guys moaning about M3's with Broken rear subframes, cooked diffs, etc - you can do that in any car if you drive it like a savage, launch it like a twit, and do donuts like a braindead heathen... I can show you stock M3's with broken subframes from launching on semi's - not the car's fault, but the driver - you never side-step the clutch on a car when launching. ANY car will break when you treat it like that - especially when you run sticky tyres that can't break traction. There's an old saying that says "met geweld kan jy jou vinger in 'n donkie se gat ook afbreek"....
Fact remains that when treated with mechanical sympathy and some sense of restraint, an E46 M3 can handle silly amounts of power being channeled through the drivetrain.
The HPF twin GT22 kit looks nice enough, but those turbo's are too small and choke the motor up top, causing it to peak earlier - not something I would personally go for - but by comparison, go check out the larger single turbo conversions utilizing GT42's and so forth - the graphs on those conversions are still climbing by the time they hit the 8000 rpm limiter.
To all the haters and naysayers - go for a drive in an E46 M3 turbo with a nice big turbo that makes peak power at or beyond 8000 RPM, and then tell us again how the engine has lost it's rev-happy character.