The Maxima is an awesome ride, definitely above the rest when compared with dumpy boring sedans like the Camry (blecch)... but comparing it with the IS? Screw speed... it's all about which one is the sweeeeetest !!!
The 2000 Maxima SE Auto was the only other car I test drove and that was because I had a 92 Max for eight years.
For me, there was NO comparison. Yes it was fast but not much faster than my 92 (had 190HP) and the auto tranny was no great shakes - the IS transmission is much smoother. Also, obviously, the handling was much worse.
And lastly, there was the intangible factor: the IS was new, cool, the interior is awesome (again comparing to the Maxima).
And the cost was not *that* much more. Invoice on the Max was 27,000. My IS was 32.8 after discount...For me it was certainly worth the extra 5.8K.