I've seen a comparison of dyno runs done on the same vehicle with the same engine and mods on both the Dynojet and the Mustang dyno. The weather corrected HP/TQ numbers were 6-7% lower on the Mustang dyno across the whole rpm range so that gives you an idea of the difference between them.
Yeah as much as I'm gonna hate not having a dyno graph reading 300 at the wheels to brag about (unless I'm extremely lucky), I'd rather have the quality tune at this point from a quality shop....and a nicer driving car will do nicely too.