There is a lot of Centurion expertise around here but I'll start you off with one opinion.
The Ironman is the better bike and a fair deal at $300. Not a steal but fair. I've never used Suntour GPX but don't believe it to be the level of Shimano 600 or 105 which you often find on an Ironman.
The Lemans is listed too high and only worth low $200s. We've had one on Houston CL at $250 forever.