If I was building a race engine using factory stroke and bore - then the 340 has the better Rod/stoke ratio which means it will survive better at higher RPM.
The 340 also also more oversquare making it suitable to RPM higher.
HOWEVER - If i was building a streeter - I'd opt for the 360. More torque due to stroke and CUI, cheaper parts, and it will make power where you can use it.
A lot is made of the bigger mains on the 360 and the greater inertial friction - but I reckon the cui and storke of the 360 outweighs any minor disadvantage of larger mains.