i think the z responds better to n/a mods. i gained alot (relatively) from my n/a mods. the DE has the best tq out of the 3 motors but not as good top end. that can be fixed, and well mine has

i gained upwards of 50 hp and 45 tq over a average DE dyno with just 3k into mods and tuning software/tuning. who knows where ill be after the new additions, i could be close to the 300 mark. the revup (in the 06 mt, and aniv. editions) will put down more hp then my motor but i have not seen few car close to the tq mine puts down. the revup has longer runners in the plenum in then the DE and that seems to attribute to better hp numbers. the HR is great outa the box but it also has almost perfect equal length headers (unlike the de and revup) and gains are better with exhaust and test pipes but not with after market intakes. the hr also looks like their AFR is pretty much around the 13 mark even after mods so who knows how much it will benefit from tuning. i would also like to add the compression is higher on the HR (10.6). mods will be cheaper for the de and revup then the hr bc the hr is newer. plus there has also been more trail and errors with the older two engines so it would be easier to make educated decisions with mods on those engines.
its going to cost you at least 10 grand starting from scratch to boost a Z (with doing the work yourself). i think some boosted DE guys have seen 550 (a car from Z1 is around that mark on a turbonetics single) on a stock block but i just checked their updates and a few guys have blown their motors. i would say to be safe you wouldn't be smart to push past mid 400s on a stock block.
if i were you i would go with a c5 vert. you get the drop top and the sex appeal but that motor responds well to boost and n/a mods. plus the n/a mods on a ls1 show better gains for the buck. who would ever suspect a 385whp c5 vert with a cute little asain girl driving it (and all that power with i/e/h/heads and cams)?
the Z wiki is your friend for the tech aspects of all 3 engines.
note: i pay 290 for both goat and Z a month. full coverage and im 23. i dont think its that bad.