You can achieve the energy rating you want regardless of method used - timber frame, block, ICF etc.The key is attention to detail.Have the project planned before you start and ensure that what you have specified in terms of insulation actually goes in.
Also give careful consideration to the design of the house - larger windows south facing, minimum windows north facing (if any triple glaze them), type of heat source (there are a million options these days) etc.
The advantage of blockwork is that it allows concrete first floors, hang items on the wall where ever you want and personally I