I voted for 3/4, but most all of mine are 7/8" with a slight cup.I have been doing some testing with fork width and fork tip thickness. I don't have a chronograph so my thoughts are based on a guess.
It appears to me that the least amount of contact between the "rubber and the road" the better. I see a lot of rubbers completely covering and hanging off the tips. My feeling is that the "stretch and friction coefficient" at point of contact would not be consistent. Does it make that much difference? Who knows. I have said before, the only thing consistent about my shooting is my in-consistency, so I want to eliminate any variables that I can.
I shoot both ways, sight and instinct. With my sighting method, I use the tip of the top fork as a sight .. With "sighting", the fork width plays a huge difference.My favorite band set is 7/8 x 5/8 x .040. With my fork tips being 7/8" and slightly cupped, there is just the tip and edge of the band to see. If the frame is the correct frame for my form the tip will be "spot on". If I change my bands to a 1/2" gum rubber or 107's then my "spot" is much bigger and I am not quite as accurate. The intersection (corner) where the band and fork tip meet is now my spot. If the lighting and other variables are good then I can sorta use that spot like a cross-hair.
If the frame is not correct ( distance between forks) for my form I have to accommodate for that and "cover my target" with the tip.Depending on other variables (lighting, target, distance) my "sight" is really a guess. I believe that there is a "perfect frame" for each shooter. Some like wide forks and some like narrow.
If the frame is good for me then it is just "point and shoot". When someone says " Oh man, this is one accurate Slingshot, it just about walks to the target and pushes the ball in" or "I like this thing but can't seem to hit anything with it". I believe that these are two examples of whether or not the frame has the correct deminsions for the particular shooter.
As far as "fork tip width" I feel that the fork tip and band width should be as close to the same as possible.If you use mainly 107's then the tip should be closer to 1/2'.
If you are not too concerned with consistent accuracy then none of this really matters.
This is just my opinion, based on my experience .