1.02 is perfectly stable. If I were you, I would not go past that firmware though. Having said that, if everything is working fine for you as is, why not just stay where you are?
My original was an A1 with 1.02 on it. Ran perfectly and had an uptime of 36 days before I decided to flash it to 1.21NA...once I did that, the router would reboot every 3 days or so and usually when hitting the wireless hard with transfers etc. Upgraded to the newer beta's (1.22NA 03 etc) and it would no longer reboot as often but then the wireless would drop thousands of packets and errors galore (I had virtually zero with 1.02).
Eventually, D-Link swapped me out for an A2 and no difference so I went out and bought a Linksys WRT610N and I have had zero issues and everything works great.
There's my story and now with the ability to flash backwards, I may try that and see if I can find a way to go back to 1.02....