Will someone please put the OP out of his misery by telling him which of the lenses he asked about he should buy?
Fine.
xtolsniffer, I used the RB system for 2 years with the C lenses. The colors produced by those lenses were beautiful. KL is supposedly the new and improved version of the lenses for the RB so I am sure you won't go wrong with either.
From what you are saying, you need only to separate the foreground from the background, and it does not sound like you are doing macro, so all this APO talk is likely abstract as it pertains to you.
Something that is far more important is the minimum focusing distance. Without extension tubes, you need at least 6' for the 250mm you mention and 11' for the 350mm. I'd opt for the 6' because I can imagine far more situations where I would want to get closer to the flowers than further away due to space constraints.
So there you have it, 250mm non-APO; that's my advice.
-Dave