I was previously a DGL-4300 user, I got it when its newly launch, right out of the box, (not only) its work and its works good! No complain about DGL-4300 at all! The reason why I decided to upgrade from DGL-4300 to DIR-855 based on a few reasons -
1) I need a wireless router which can broadcast further range with 802.11n in 5Ghz.
2) At the same time, some other devices are still only be able to work in wireless 802.11g in 2.4Ghz.
So this DIR-855 seems to be a prefect match to what I need, I choose to stay with D-Link this time as I was having great experience with DGL-4300. The DIR-855 fautly router offer very poor wireless signal as compare to DGL-4300, I do not know what exactly went wrong at that time, and I go ahead and purchased a ANT24-0230 (Xtreme N 2.4GHz Antenna) to see if it would help, and of course, for using the ANT24-0230 with DIR-855 would totally defeat the purposes of why I pick this router, later I found that the router has known problem and is being recall by D-Link, so I try to contact D-Link to arrange a RMA, after a series of drama, I got my replacement router. (for detail, you can read from my other post - subject - Recall Status...)
After I received my replacement DIR-855 router, as Mlachake suggested, rather than using a saved configurations from the fautly router, I go ahead and configure everything from the beginning, one thing that I believe most users are aware of and do not like it, is that - why is now, both wired and wireless get grouped together in the MAC address control filter?
So far, the 2.4 and 5.0 Ghz wireless signal works great, by mean, one of my computer (connect via 802.11g/2.4Ghz) that is located 2 floor away from the router is able to receive constant 4 out of 5 bars signal; at the same time, my MAC Book Pro OS 10.5.2 (connect via 802.11n/5.0Ghz) that is also 2 floor away from the router is also able to receive constant 4 out of 5 bars signal as well.
By now, I can tell that, this replacement DIR-855 router can provide further wireless range than my previous DGL-4300. I have not yet test everything I want on this router yet, but in terms of its wireless performance, it is working the way how D-Link claims it should be; 802.11g 2.4GHz & 802.11n 5Ghz are simultaneous working on this DIR-855 router.