The 3400 is not a bad engine to start off with. The head gakets are fine on them, but the lower intake gaskets are known to go. My motor is amost at 80000km's (known to go) so I've pulled it out this winter to change it before something really bad happens. Only concren is GM had to re-design 3 times before they got it right and the intake kit up here goes for $121 CDN (upper & lower) .
Now if you want to boost the motor, that will take more work. In stock forum, 60degreeV6 forum guys say it can handle 5psi (7 most) without issue of blowing things up internally anymore and you have to do internal changes. If you want a performance cam, you have to send your's out to have a regrind done. There have been talks about one company possibly making cams for the 3x00 series motors now. If you really want to boost the motor, get a 3.1L block and stick the 3400 top end on it, this will bring your compression ratio down between 8 - 8.5:1 roughly, this will take more boost. I've been wanting to boost my motor but lack of funds right now and reaserching what others have done.
Reading the other post, you want roughly 400HP. I'll be happy with 300 myself. Even the 4T60E would need to be rebuilt to handle that kind of power. I'm also with a Grand Prix Club (wife drive an 02 GTP) and these guys that turbo thier motors break the tranny. Once the tranny doesn't break anymore, stock up on axels!

I think 300HP will get me low 13's which is good enough for me, currently doing 14.2's. If you want 400, I'd recommend going with the 3800S/C, use OBDII computer so you can get your 4T60E tranny and there's HP Tuners for software programming.
Also, the motor with the red intake and valve covers are powder coated. The 3400 SFI was sanded off, then put into a sandblaster with heavey blasting beads to give that rough look again, then out for powder coating. I plan on taking the 3400SFI off my motor this year too, as for colour, not too sure yet.
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