A car like the IS should be able to keep up with same year GTOs and Mustangs. It's pathetic that they cannot come anywhere close to doing so.
So what is the problem with a v8 IS?? Sure, it would cost more. But you don't expect to get the extra 80 HP for free do you? BMW owners buy M3s, and Lexus owners would buy a V8/IS for the same reasons.... except they would not have to wind the crap out of the V8 to get that good power like M3 six needs.
Ever hear of a BMW 540? Pretty great car. Well it is just the 525 with a v8.
How about a GS400 vs GS300? Which one would YOU prefer to drive? Same car, but one has a v8.
Even the dumb Americans have put inline six and V8s into the same car... since the early fifties. Since the Lex 6 and 8 weigh the same, there is no down side except cost.... unless you care about hurting the feelings of Mustang/GTO owners when you dust their butts!