Standard GTI on our dyno made 198.2bhp on Saturday, PD140 audi a4 made 142bhp and a standard ED30 made 231bhp last week.
strapping cars may be one thing, but as long as you strap according to the way that DD instruct you to do so durung your training then you cant go far wrong, most cars we run in 3rd gear, if strapped and loaded up correctly with the correct settings in the dyno then wheelspin isnt a problem, wheelspin is obvious. When you look at a graph and the operator will see it instantly.
I know a fair few Revo dealers that also see a consistent 350+ from stage2+ on a dyno dynamics dyno so its a mystery. We have a customer that has an s3 with stg2+ software, it made 357hp on ours and 398hp on another local dyno (not dyno dynamics) so shows that some will read sensible figures, other tuners use their dyno as smile machines
Choose your tuner, use their dyno for comparisons before/after mods, dont bother going 'number shopping' around dynos and you will get a good consistent repeatable comparison.