Brady, the references I have indicate that the US 76L54 and German 75L48 are both at about 5.7 or 5.8 kgs for an HE round. This means they're roughy equivilent, with some variance for casing thickness and explosive material. Figure close enough for anyone but the supremely anal-retentive (eg, much of this board).
The M18 would do well, but would require carefull handling to survive. The 76mm gun with standard APBC would penetrate a MkIV at 1500 meters or less most of the time. But anything bigger than a .50cal would kill a M18 at any angle, almost any distance. It had about 15mm of armor in most places.
Agreed on the tank types. HTC isn't getting into anything like the Panzer Elite or Combat Mission level of detail, but they do a pretty good job with the vehical models. Still, I suspect it's somewhat easier to add vehicals than aircraft, if only because the FM details on an aircraft are so much more finicky than anything but the internal layout of a tank. Hope to see more sometime soon. Like a heavy (Tiger or KV), a fast mover (M18, M5, T-70, Puma), an assault gun (M4-105, M7, Hummel, Stug42), and a TD (Jagdpanther, JpzIV/70, Hetzer, Marder or Su-85).
Also looking for Elvis, but not holding my breath...
Thog