No difference other than the unlocked multiplier.
You say you aren't going to overclock now, but what happens down the road when you wish you could?
Sooner or later a faster CPU will come out and you'll wish you could keep up!
For the extra $20, I'd get the "k".
Almost all MoBo's now a days has an easy BIOS overclocking setting that lets you choose the percentage of overclock you want. Mine goes 5%, 10%, 15%, 20%, 25%, and 30%. They took the hard work out of overclocking now a days and have made it really simple. That CPU should easily overclock to 4.0mhz.