Alternator Pulley Size

I just went 3G on my fox. The pulley on the new alt. is about 2.75'' vs 2.5'' on the 2G. I found a deal on a 2.5'' and should have it in a few days. After doing some math,maybe i better stick with the 2.75''.
6'' crank pulley,6500 shift point,rev limiter at 7k.

2.75'' at 7k = 15,272
2.5'' at 7k = 16,800
2.5'' at 6500 = 15,600

The car idles at 1k.
With the low beams on,msd 6,340 lph pump,flex-a-lite 185 fan. 14 v with the 2.75'' pulley,at idle

A little easier on the eye,the old 2g showed every bit of it's age.

Broken,very broken. Just installed this last weekend,drove the car about 200 miles,but did not hammer it much (holiday weekend) all was fine. Was not finding much grip today. Stopped and lowered t/p on the hoosier QTP's Dropped the hammer at 40 in 2nd (4k) tires churned a little but did not blow them off. Shifted at 6600 let off,went to 4th,5th. Cruised a few miles and was pulling over to check something,when i see the temp gauge at 220 ! This is what i found. Alternator case cracked in 2 places,belt off. 130 dollar tow.

Belt tension was fine. Yesterday i was mad,and not seeing what happened clearly.
Today with 20/20 hindsight the signs were there,i just did not pick up on them. Last weekend the the rear interior plastic panels were making some noise. This did not set off any alarm bells,they loosen and make noise regularly. (the tone did seem different...in hindsight) coincidentally i noticed the vibration after dropping the hammer hard in 2nd (more hindsight) perhaps the start of the crack ? Went through and tightened the panels up this past sat.
When i started the car on Sunday,the steering wheel was vibrating (never did that before) By the time i got to the gas station,things seemed normal. Over the next 20 miles i had stomped on it hard 3 separate times and the car was running very strong. At a slow cruise,40 4th i was feeling a dull vibe. Thought maybe the exhaust had loosed up. Climbed under there did some pushing pulling,all seemed ok,checked the lug nuts,all tight. A few miles later the wot blast that caused the failure. The signs were all there...i just failed to put it all together,until after the fact. Now i am angry with myself. A coworker said,look at the bright side,it did not catch on fire or toss the alternator through the glass hood or new radiator.True that !