I rode Venoms for a long time and still race with race compound Avon's but for the street I like the Dunlop TT's. They are great in the rain, they stick great when there warm, and they have better sizes for my street applications. Your limited with sizes with Avon. If you plan on making a little hot rod that handles better. I'd put the 18 on the front. Also I'm running a skinnier set of tyres this year racing cause more than just width is weight, how fast you ride in the corners, and the right tyre for the rim. You can put a 4.00 x 18 on a WM2 on the front and I can bet you you'll never reach the edge of the tyre with out crashing. Plus there's nothing worse than seeing a guy with a sporty bike and he's noly using $75 of his $175 tyre. That's my imput, you may want to ask Joe or JD. They'll know better on which tyres let go at which speeds.
AAron