For RTL on ocf just adjust the IOL tune (can't remember exact name but it's below IOL's). Stock is 21 21 when on auto. Set 21 21 manual, reboot, check rtl/iol trained correctly. Bump both in tandem one at a time till no boot then drop one. On 6320 @3840c11 1t i could run them 27 26 making 1-2 iol. (1.8vdimm). (XTU, didn't check 32m)
As far as IMC goes, yes it does make a difference. On the 6320 i used for xtu i could run 3953 1t, on the 6700k that went in next i couldn't even do 3866 div on same boards. Be checking with another 6700 this weekend.
Totally agree on 2 dimm board, one div higher no problem.