Today, dollar for dollar, is the 318 faster than the 340 ???

I have 6 340's but even if I didn't I would find a 340 block to build. If its just a stock driver a 318 is fine. If your spending the money to do a performance build then it makes sense to go with cubic inches.
318 is a great engine and can be one hell of a sleeper. Throw on some good heads, cam and 4 barrel and a 340 pie pan and most wouldn't know any different.
Im just glad I had the foresight to hold on to all the 340's I came across in the past 20 years. I did let one go to a friend but other than that I still have every one. The 340 is just the perfect balance of short stroke and bore size.