Jesda - I'm in a similar situation. Looking to replace the SC400 and have given some thought to both an 00-01 Q45 & QX4's. Let me say, the QX4's are probably not a good idea. Slow, over priced and basically just a Pathfinder. The Y33 on the other hand is not a re-badged US model Nissan, and it has it's strong points, but keep in mind it was released as part of Infiniti's way of battling the "price issue" by mid-to-premium car buyers. I think if Infiniti had the G35 sedan back in 97, they would have never took the Q45 a 1/2 step back.
I've been looking at several different things Mazda6 wagon's, 03 & 05 Maxima's, 03-04 M45's, 02 & up Q45's, G35 Sedan's, FX's etc and I have to say nothing seems to really "speak to me". I really wish I still had one of my old G50's.
Long story short, I think the M45 is the closest to the "spirit" of the G50, but you need to make sure there's no neglect or other issues.
I'll be looking forward to some "test drive" write ups from you

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