AMD Radeon R9 200 Series in GIGABYTE Z170-HD3 motherboard?

Solution
You did not specify the exact model (only series), but it does not actually matter - any graphics card with PCI-e connector will fit into your motherboard. That means any card manufactured in last 12 years or so. So yes, you can get any R9 card from 200 series, it will fit. Just make sure that your power supply is up to the task. High-end models (290,280X) use much more power than low-end ones (250,240).
You did not specify the exact model (only series), but it does not actually matter - any graphics card with PCI-e connector will fit into your motherboard. That means any card manufactured in last 12 years or so. So yes, you can get any R9 card from 200 series, it will fit. Just make sure that your power supply is up to the task. High-end models (290,280X) use much more power than low-end ones (250,240).
 
Solution