I worked with AEM on the first stand alone systems for the Viper, I provided them with the first development car a 96 GTS. We did have a bunch of issues at first, a hardware change was needed to add an additional ground for the wideband sensors and there were some software updates, but after all that, the system worked well for big cam motors and forced induction. This system is no longer made, so the computers are hard to get.
AEM is finishing a Gen 4 Infinity system for me now on a race car, Im really excited.
The tuning business is tough, plus when you are building big power you walk a fine line. On forced induction engines any change in fuel or **** injection can lead to a failure. Tuners often get blamed for failures, some claims are founded, many are not.
I only dealt with the old RSI, but what I have heard of the new RSI has been good. Todd at AC is very reputable and I think his endorsement of them should be considered.
My 2 cents, your opinion could differ.