Does it have to be 4x-16x?
What do you consider "long?"
For me, 3.5" is on the short side for a magnum, but fine for a non-magnum. On the other hand, 3" is short for even non-magnums (at least for me.)
Taking that into consideration, take a look at the Burris Black Diamond in 4x-16x-50mm. I have one and, although I haven't measured it, the eye relief is just fine to me and what I would think most shooters would consider long.
The Bushnell Elite 4200 in 4x-16x-50mm is either 3.5 or 3.6"
Now, if you want longer eye relief, and don't mind if the power range varies a bit, take a look at the Leupold Vari-x III in 4.5x-14x-50mm. I have one in the Illuminated model and it's eye relief ranges from about 3.6" to 4.6" (Don't quote me on that though, so go to the Leupold website and make sure - but I know that I'm very close to those numbers.)
The Leupold Vari-X IIIs have some of the longest eye reliefs available.
Zachary