Thanks, this is some very interesting data. I wonder why Fastcraft reduces the framerate (compared to vanilla I think?), which would be something to fix. You may also want to try the asyncCulling option in the FC config to lower the calculation overhead, although that's quite experimental.
A sampler report (sampler download -> opening post) generated by "/csampler report <filename>" from your typical benchmark situation in the FC 1.22 case could be interesting as well.