Is it okay to remove the backplate from my GPU?

Solution
If you can tell it will fit without the backplate, then you can do that. Quite stupid though that it simply doesn't fit at all.

Could also use the PCIE Express 1 x 16 slot below.
The general rule of thumb is, for every 10C higher, component life decreases by 50%. This has nothing to due with GPU's specifically, but electronic components in general. That card will no doubt idle and run hotter under load, without the back-plate. I wasn't trying to be an alarmist. Merely pointing out that removing the back-plate was one of the least favorable ideas offered.