If you want the absolute differences between the amps, read my in-depth review of the Road King II, which fully details the differences between the Road King, Road King II, the Road King II version 2, and the Roadster:
http://www.musicplayers.com/reviews/guitars/2006/0906_MesaBoogieRoadKing.php
The Roadster has the same clean voicings as the Road King II, which are the same voicing as that found in the Lone Star. The only difference is that the Road King II offers different power output options -- EL34 or EL34 +6L6 vs. the Roadster's 6L6-only configuration.
As for the comment from someone who tested the amps side-by side, there are other contributing factors that could account for a difference in tone, assuming the cabinets were the same:
1. Assuming both amps were set to 2x6L6 or 4x6L6, one amp may have been set for Spongy instead of Bold.
2. One may have been set for tube rectification; the other set for Diode.
3. The Road King has TWO effects loops, with the second following the first one in the signal chain. Depending on settings for your sends/returns, with or without gear plugged in, if the loop was engaged, then two loops were in the circuit in the Road King whereas only one loop was in the circuit in the Roadster.
Hope this (and my review) clears up the differences (and similarities).
You can make the Road King sound utterly non-Recto in tone if you want. It's just incredible sounding.
Scott
