What ISO should I use for startrails photo?

First off, I know about the startrails software to stack mult. Exposures, and this time I want to try to do it in one exposure.

Here's what I will be using:
-nikon d200
-18-55mm
-shutter speed: ~65 mins

My question is. What ISO should I use for this long of an exposure? When I use startrails software I shoot at ISO 6400, at 30secs each, but I think that might Be tops sensitive for 60 mins. I don't want to screw up this thing that will take this long to do, So could someone help?

Oh yeah, and I will be shooting after dark, so 11:00 and later.

Added (1). Like I said, is am NOT doing a stacked photo. And btw, the 30 sec photos I did with this photo where at ISO 6400 and it's not too sensitive for that

That would be Way too sensitive for that long of an exposure. Try something more like ISO 100 or 200.In addition, the sensor will get hot over the length of that exposure, and you will get artifacts. I would recommend doing back-to-back 30 second exposures at ISO 200.

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