Upgrading to 5 lug will give you the same wheel choices for Ford, Toyota Supra, 300ZX, etc. You can get some great (but expensive) wheels for your Z from the likes of Volk Racing, Work, CCW, HRE, BBS, etc, after you do the conversion. Just measure the offset what you need and then order the wheels.
FWIW, Mike was only giving advice. If he needles you, it is because he likes you. He just runs over the people he doesn't
Davy