If you overclock, you might be able to get 2.6GHz out of the 3800+ (that would make it a 5000+) for no extra charge
Or if you want more, go for a cheap Opteron, and overclock that.
Some Opterons can do 2.8-3.0Ghz (even the cheapest ones)
Even if it does only 2.6GHz, you still have a FX-60 for a fraction of the price.
2.4GHz = 4800+
2.6GHz = FX-60
2.8GHz = FX-62
Think it over
My next upgrade will most probably be an Opty 1210