Well, we know a Ferrari 458 GT3 can do a 2:04.9 versus a 2:06.8 for a V8. There must be a comparison of the speed of the Fezza to a DTM out there somewhere.
V8's would wipe the floor with the Ferrari if they had similar tyres. The dunlop control tyre the series runs at bathurst is a heap of crap. Virtually zero feedback to the driver. The softer compound they've been using at other circuit is alot better and actually provides some great racing, but the idiot organisers refuse to move to it as the main compound because for some reason they have it in their heads, they're the second coming of F1.
Also Bathurst is not an aero track. I could count 4 corners where the aero advantage would come into play, but otherwise they'd be blown away on the two 1km+ straights.
It would be close and I might even be in favor of the DTM car, but it wouldn't blow them away by 2-3 seconds.