Regarding the TAS debate all the data I have points to increased TAS with increased temperature, however the manifold pressure must be increased to maintained the same percentage power.
The only similar data I have at hand is for the Piper Lance,
0 degrees C @ 6000ft and 65% (22.3 MAP @ 2300RPM) = 142 KTAS
30 degrees C @ 6000ft and 65%(23.3 MAP @ 2300RPM) = 147 KTAS
For the Chieftain,
ISA @ 10000ft and 65% (29.8 MAP @ 2300RPM) = 184 KTAS
ISA +20 @ 10000ft and 65% (30.9 MAP @ 2300RPM) = 187 KTAS
This was just some quick POH research, in the real world there are lots of other variables.
If you maintain one power setting (manifold pressure/RPM combination) for all temperatures you are not maintaining a constant percentage power output and at higher temperatures your TAS will suffer.
Weight will definately have an impact on any aircraft TAS for a given power due to the increase in angle of attack required to generate more lift to balance weight.