Processor Comparisons

Hello,
Has anybody recently performed a comparison of the major FO processors available, in terms of performance, conformance, reliability and cost?

I'm mainly interested comparisons of RenderX XEP, Antenna House and Apache FOP (0.2x or 0.92 or trunk?) as I require PDF and PS/PCL output.

Interested to see what research is available.

Thanks,

Tristan Stevens