As a bit of background, I am a virtual employee working from my residence. I work in the wireless engineering group of a major computer company. So I am constantly on one of several computers and require a high degree of reliability and performance. In addition to computers I have several other devices on my wireless network - three printers, TiVo, couple iPhones/iPod Touch, personal weather station, etc. My wireless system has grown and morphed over 10 years of usage.
I appreciate you don't want to run wires. I did run one Ethernet wire - to interconnect two access points at either end of my long one story ranch home. The two access points provide great coverage. These are apple dual band units.
I also have a Hawking 802.11n repeater that I use in my motor-home when traveling and to provide good signal to the back of the property when at home (the motor home is stored at the back of the property). I use either the standard antenna with the Hawking unit, or optionally an external Yagi antenna for very weak signal RV parks. The Hawking repeater works very well - the throughput and latenacy issues are minimal, the reliability of connection is very good. One does not know if connected to the Hawking or one of the two in the house access points.
I would suggest for your senario to consider one Ethernet wire to connect two access points, or try a Hawking repeater.