No experience with the ZR1, but I had a supercharged '07 Aston Martin Vantage with 625+ hp, which is a very similar car in many respects to the ZR1. The GTR is a much better DD in almost every way. It's easier to drive, much better in the rain, faster in all situations (now that I have a midpipe/tune), the electronics are much better and always work, I can park it anywhere without having to worry about it, the doors actually lock, it's more confidence inspiring and tossable, gets better gas mileage and has a longer range, and the shorter overhang means it doesn't scrape the front going in and out of parking lots and driveways, so I don't have to plan out which parking lot entrance I will use whenever I go out. I could drive it every day, but I don't.
What I miss are the sounds it makes...the GTR is sounding pretty good with the midpipe but still no match for a good V8, and some aspects of the interior, especially the leather seats. The interior is not as much of a step down as you might think, though. The only really glaring omission on my '11 is the black plastic AC panel, which was easily fixed with a carbon overlay. And that Vantage is a looker, too, but I have to say I really Iike the looks of the GTR, especially in red. Other pluses for the Vantage are much better paint quality, more solid feel of the doors, and hood struts (which are available in the aftermarket but I still don't understand why Japanese cars never have these). The 6-speed was good but I prefer the dual-clutch and paddles. That's all I can really think of.