Hi Scooby,
Welcome to the forum. I've had my 370z GT ultimate now since march and love it. Having had a 350z before it was the right choice for me. Mine has orange interior which i like as it seperates it from the standard zeds.
Power wise its a very smooth power being a big grunty engine compared to the scooby, but it just has buckets of torque no matter what gear your in.
With regards to the nismo, the mk2 i feel is sexy but the mk1, which i didnt used to like, i've grown to adore it. Just think its more in your face, but at the end of the day its personal to you.
Def on the exhaust though, you will want to change it. Ive just fitted a 2015 nismo exhaust to mine and it suits me perfectly,tips dwarf the oem exhaust and most aftermarket looks awesome. The nismo should have more noise though than standard.
Would i buy a brand new nismo over a used zed and mod to supercharger or turbo?? Probably not but its all a pipe dream for me anyway. You could have a stealth gtr killer for same money. But ultimately your choice. Try see a few before making your mind up.
Hope this helps