Well if your ambient temperature is 90°F, thats definitely not going to help things, but you can still run an overclock depending on the temperatures you are getting. It really just depends on how good your air-cooling is and what temperatures you find acceptable.
For CPU's if you are using an Intel, the overall consensus, and typically the advertised safe thermal level is 70°C. Obviously this can very a little between different models, but that seems to be about what most chips can do. To be honest I have no idea what the safe temps are for AMD chips anymore, as I haven't used one in years, google is your friend here. If you are seeing temps at or above this though, I would suggest moving down to stock speed, seeing if that gets you in a decent temperature spot, if it does great, if not, underclock.
As for GPU's, most modern GPU's have a safe operating level at around 100°C. So technically if you really wanted to, you should be able to run them that hot, from what I have heard the 290x's are running in the 90's right out of the box. I personally don't like running them that hot though I typically try to shoot for the 70-75°C range on air. So its really up to you, but just as with the CPU's if you are under your desired temp, keep it there, if you are above it, slowly notch it down until you are.