welcome...I owned a zx14 07 with sec flies out,PCIII and slipons and -1 front; even with that setup I guarantee you :my stock busa feels much stronger.
Check the guys who owned a zx 14 and own now a busa2; none of them will claim that the zx was stronger, but the zx do have better ergonomics and their brakes are superb !
If he had that much done to the bike and you won? Then he wasn't a good rider or his bike wasn't tuned. There is no way. Looking at the stock specs betweent the bikes, anyone who has ridden bike for more than a day will tell you, there is no way to tell which bike will be faster. Some might disagree and say the ZX14 would be faster due to the Busa weighing and extra 50lbs. But all that aside, his bike should've been faster than that, or he sucked.
As an owner of both bikes, an '07 ZX14 (lowered, otherwise bone stock), and an '08 Busa. If being completely honest, the ZX14 noticeably feels like it pulls harder. Thats my opinion and the opinion of two other friends that have ridden it. Racing my busa 1v1 against my own ZX14. Whether I'm on the ZX14 or the Busa, I win against everyone I ride with which is only 4-7 people depending on the day. I'm not saying I'm an awesome racer, I'm just better than they are, I play harder if that makes sense.
Which bike is faster in my honest opnion? Neither bike, the conflicting "fastest bike" title is evident when comparing magazine articles. The faster bike will be the Bike with the better rider is both bikes are stock. No one can argue this and if you do, you have the shade pulled over your eyes.