I got a DIR-655 as well about a month ago (A4 revision). Assuming you use an adapter that supports 40MHz over 2.4GHz, then you can get the full 300Mbps connection. On my laptop, with WPA2 AES, I can get like 10MB/s from my desktop to wireless laptop. And that's running a mixed setup with 20MHz for 802.11g clients as well. Apparently if I ran 802.11n exclusively, the speed would would increase quite a bit.
It should be noted that 5.8GHz (aka dual-band stuff) doesn't penetrate objects as well so it could be more problematic. Even though marketing hype claims its so much better.
I find this place does the best reviews for routers:
SmallNetBuilder and if you just want to quickly compare speeds:
SmallNetBuilder - Wireless Comparison Charts
Though I agree, running cables is the best way. I have cables ran to pretty much all rooms other than the kitchen/bathrooms. Fast, reliable gigabit speeds throughout
