68 truck 318 cam. How big can i go?

I don't mind bumping the compression by milling the heads, but I'm wondering if a bigger cam than they used would be hard to deal with on the street. I think I can get the heads to flow at least as well as they did. My truck is pretty light and has 3.73 gears, and getting going with a stupid big cam shouldn't be too bad with a 7:1 first gear.
I drive about 30,000-40,000 miles a year in my '68 or my '70 powerwagon with a 383. Both are rock solid reliable and I've rebuilt/replaced most of the running gear and most of the engine systems. I'm getting a game plan together for the '68, which will be my hot rod.