The stock Z is a great N/A Crossfire matchup, especially since they're very similar in application (2-door sporty N/A coupe).

Numbers-wise a lightly modded Crossfire should be somewhat comparable to an old base, stock 350Z, with a slight horsepower advantage to the Z.
After 2005 the 6MT Z's engine was slightly improved (mostly tuning) and I'd start to worry a lot more about them.
The 2007 Z with the VQ35HR is definitely winning the horsepower game by a wide margin.

If I were up against a Z with an automatic I would seriously try to beat it, otherwise it'd be up to the shifting ability of both drivers and a race would just be close enough to be fun (I sure wouldn't put money on my Crossfire).

The 350Z tuner market is much bigger, though, so there are lot of beastly Zs roaming around.

Midrange 3-series BMWs (328, older 330) are also decent/fair competition but 335s are definitely well into SRT-6 territory.