It seems that the most-recommended light in that size class recently is the Emisar D4, which I recommend as well. With the 18350 tube, it is about the same size as your PD20 (quite a bit shorter, but slightly fatter head). When you remove the battery or unscrew the tailcap slightly, it will come back on at around 150 lumen, which is the same as "high" mode on the RC09 (~3 hours runtime on 1 18350 cell, or 8.5 hours on one 18650, which is a longer cell). But, the user interface will allow you to ramp smoothly down to <2 lumens, and up way over 3000 lumens (very short runtime on the high-lumen modes--the thermal control kicks in quickly to lower output and keep it cool enough to hold). It comes in 3 body colors, a bunch of LED choices, and seems to be available now from intl-outdoors (maybe some also from mtn electronics).
For under $160, I'd splurge on a pair of lights, maybe in different colors and different LED to match your moods (for example, the HI version, $58, and a 219c version, $40), a couple of 18350 tubes ($10), six Aspire 18350 cells ($30), a pocket clip (mtn electronics sells a "DC-CLIP-1" that works, $1 plus shipping), and a pair of XTAR ANT MC1+ chargers ($8 ea). You could throw in a passel of 18650 cells to use when you wanted a longer light with a longer runtime, and still stay under $200. The "save money" version is only 1 light, 2 cells, 1 charger, and a clip for under $80.
I LOVE spending other people's money!
Best of luck, and enjoy the research!