Definately get the 80mm. As for the Shroud I see No need yet. Now of course my cpu is not an XP but a Standard Tbird 1000 @ 1.3, running 1.8 volts. Two 80mm fans sucking in at the bottom, 60mm directly behind the cpu for Exhaust. 2 power supplies set to exhaust and 2 80mm fans right above the 2nd PS set to exhaust. Idle temps 30-33 and full load has not gotten above 43 yet. Best of all it is super quiet. The loudest fan in my case is the one on My Geforce2 GTS. BTW my fan is turned and it is blowing into the SK6