I got the numbers for everything but 986 from youwheel.com....car-body-torsional-rigidity-a-comprehensive-list. 986 wasn't included but according the Excellence Magazine Boxster History page, the 987 is 4% stiffer. Therefore (987) 12600 Nm/deg divide by 1.04 gives 12115 Nm/deg for the 986. Not to bad really.
  Still wish the roof wouldn't creak when I exit the driveway.
Lamborghini Countach	2600 Nm/deg
Honda S2000	                7100
Mazda MX-5 (NC)   	8132
Lotus Elise	               10000
Porsche 986 Boxster	12115
Porsche 987 Boxster	12600
McLaren F1             	13500
Ferrari 360 Modena	23000
Porsche Carrera GT	26000
Porsche 987 Cayman	31500
Perhaps you can draw the conclusion that if 13500 is good enough for the Mclaren F1 then the 986 is 90% awesome