The main difference between an inline4 and a v-twin is the rpm limits.
You can get into the bore n stroke of each motor and that all has a big part of it too, but thats a whole nother discussion.
I4s make some crazy HP at rpms that a v-twin will never see, now I'm talking stock motor to stock motor.
But the v-twin makes crazy torque off the line and most hold it to at least 1/2 to 3/4 rpm range.
Torque is what gives you acceleration to a certain speed, HP is what keeps you at a given speed over distance.
So the whole "sport bikes are no fun going slow" is because of the lack of the trq that the v-twin makes.
So its a classic trade off, I4 if you want to blast down the road at 150+ mph, or v-twin stop light to stop light fun.
But also be prepared for the somewhat lack of aftermarket support, that you get from the main 4 Jap factories, Honda, Yama, Suki n Kawi.
Most of the aftermarket we get is someone thought something would be a good idea and found a way to make it happen out of their garage.
To me it just depends on what you have fun with.
My 2 track days I did, I got passed on the front straight by a # of ppl, got back into the turns and I lined one up after another and pass them right back.
I know I'll never do 150+ mph, and am completely ok with that.
I guess I really am getting older now.
Anyway, just my $0.02
Gl hunting