How fast were the planes going and why is there is a pretty wide variance

Flight 175 flew as fast as Colt .45

Which speed numbers do you use.. NTSB - NIST or WIKI or lower yet Shilley Walker's numbers

WIKI 2006 numbers 
"Flight 11 was traveling roughly 490 mph (790 km/h) when it crashed into the north tower, Flight 175 hit the south tower at about 590 mph (950 km/h). " 

http://web.archive.org/.../Collapse_of_the_World_Trade...

.......................................................flight 175 .......Flight 11
1. WIKI ......................... ............. ....590 mph 490 mph
2. "Radar Data Impact Speed Study" .586. ..... 494 
3. NIST ......................................... .542 and ......443 mph 
4. Shilley Walker ..............................530 and ......400 mph

" .45 ACP pistol round has a muzzle velocity of 850 ft/s typically. That translates to about 580 mph."
.45 Colt 
http://en.wikipedia.org/wiki/.45_Colt

bf (540 J) of muzzle energy at about 860 ft/s (260 m/s), making it roughly equivalent to modern .45 ACP loads. There are Cowboy Action Shooting loads which develop muzzle velocities of around 750 ft/s (230 m/s). Some handloads and factory manufactured cartridges put this round in the same class as the .44 Magnum.

.45 Colt 860 ft/s (260 m/s) = 586.364 MPH muzzle matches 
NTSB concludes 510 (586.898 MPH) by 0.534 so a plane few as fast as .45 Colt flies thought air ?