Yes, It seems to be.
I got those kind of temps on my FX6100 on a stock heatsink.
I got as high as 4.85Ghz using the stock heatsink but the temps where really high on heavy loaded benchmarks and a few times it had shut the machine down.
Really high like much more than 70 degrees.
I know that is pushing it and I have had them up there quite a few times trying to get a peak overclock.
I think close to 90 without stopping the benchmark a few times.
But I don't advise letting it get that high at all !!!
AMD's max temp spec is 70 degrees and that is were I tried to keep it as a maximum.
With a Corsair H100 cooler I can keep it between 63 to 69 degrees at 4.95 Ghz on very heavy loads and 25 to 28 (ambient temps) at idle.
I have had the FX6100 to a little past 5Ghz but the high temps made it unstable with a heavy load.
At these settings the CPU voltage is quite high as well ( 1.58v to 1.62v) and is the main cause for the high temps.
Watch your NB voltage as well as just increasing this alone can cause your temps to skyrocket on a high overclock without touching the CPU settings.
It takes a lot of patients and a lot of resetting and starting over due to lockups too find a happy medium running that high.
Mine will run 4.95 all day but I backed it down to 4.85 to 4.88 for a little better reliability as this allowed me to lower the voltage a bit as well keeping it below 60 degrees.
I don't do games on it but as I mostly use desktop business apps and video stuff, So the benchmarks are the hardest apps it will ever see for the most part.
I think 4.75Ghz was about the best that I could do on the stock heatsink without worrying about killing the thing.