I cut the AE tables by a bunch and the car seems to drive okay with the progressive linkage. On my setup the secondaries start to open at 33% on the TPS. You can adjust that number a little bit by changing the length of the link.

It cruises down the freeway at around 15% TPS so it doesn't really need the rear throttle blades most of the time. Only issue I can think of with progressive linkage is that the rear injectors aren't doing anything much of the time so they might have a problem long term. It would seem better if the rear injectors were firing at a very reduced rate below the 33% throttle position just to keep the fuel fresh and to keep everything working.

The guy I talked to at Holley strongly recommended against using progressive linkage. I'm going to drive it for awhile and then switch back to 1:1 just to get a good feel for both.