The reason I'm asking what you shoot is that if you're shopping for a new camera, you need to decide whether you really need another dSLR or whether a mirrorless system would better suit your needs. I've been shooting Nikon dSLRs since the D70 came out in 2004, and I have lots of glass, speedlights and other accessories to go along with my current D810. But I still like the concept of (sometimes) traveling small, light and simple. Companies like Fujifilm, Ricoh and Sony (I hate their menu system) make some pretty remarkable mirrorless cameras, both with fixed and interchangeable lenses.
So, some questions to ask yourself:
- Do I have a lot of money already invested in Nikon DX lenses?
- What focal length range do I need (want)? Or, looking back through my past photos, what focal lengths do I use most often?
- How would I feel about not having any zoom capability? What if that meant that I could get better image quality if I didn't have a zoom?
- Do I like shooting in low light and at night?
- Do I prefer to pack, travel and walk light?
- How many of the features of the D5100 do I currently use?
- How is my eyesight? Can I live with a camera with just an LCD display (no viewfinder)?
- What shots am I missing with my D5100?
Good luck in your search, and make sure you keep the "enjoyment factor" at the top of your list.