Well good luck with the new to you ride. The Cobras wiil most likely be a bit louder. Do you know if it has the goats belly (big chamber that is under the bike, connected to both exhausts) If it is there, it's still be a little louder than stock, If it's NOT there, it will be alot louder.
As for the speed and acceleration of the Vulcan, it is one of the fastest and quickest in it's class. Not that it's a rocket, but it can hold it's own pretty good. Fastest I've had mine was just about 110mph on the speedo (177kph) But that was on open road, not a track, where I'd probably try to get it going as fast as possible!
Here's some numbers posted awhile ago between the different Kawi's....
Always good to know we have the fastest of the Kaw Cruisers (well except for the Meanstreak)...
This info is dated, missing the 1600, but still is interesting.
Quarter mile elapsed time/ending speed
1500 Mean Streak 13.76/95.6
800 Classic 14.34/89.9
1500 Drifter 14.56/88.9
1500 Nomad FI 15.49/88.1
800 Drifter 14.56/88.9
1500 Classic FI 14.98/88.7
1500 Classic (carb) 15.03/85.3