these are very usable data.
Some tests of my own to regain a few hundred rpm.

The A-type muffler can be dismantled into parts by removing the three screws, filing off the crimp,and slowly heating, until the epoxy gets soft.
Carefully wiggle the added damper off.
Ream the exhaust outlet out one millimeter. This compensates for the higher back pressure in the added chamber.
Using a 30 degee cone punch, form a bell mouth on the inner side of the stinger pipe.
With a suitable rat-tail file, ream the stinger pipe about 0.5mm.
Using liquid metal (market dependant), glue back the added damper, well lined up, and screw tight while the glue is still uncured.

After these mod's the exhaust note still is very agreable, and power loss is very much reduced.

Field data:
Engine .21 mvvs, MA 8x5 (1/12 combat, 85/15 fuel, no nitro) 16400 -16.600 rpm with standard 3235 muffler
This is ~500 rpm in excess of ACES regulations.
The modified 3235A-type muffler turns just around the limit of 16000 rpm (pinch-peaked, cold, 16.200, very hot 15.890) A silicone deflector will take care of the extra 100 rpm.
Noise is very much reduced by some 5 dB(A); it was 84 dB with the 3235, now it is 79 dB at 7 metres (77dB with non-modified 3235A-muffler)