Thanks for the response.
For what it's worth, since WF5 I routinely optmize on upto 9 parameters generally using a failure_index<1.0 optimization criteria. I do find "9" taking painfully long, especially when hours into it I find I did something that won't work (like not provide enough range for dimensions and model parameters to change in). To be sure I am happiest 6 parameters or less. I've tried using exclusion for singularity areas... it is not worth the computational overhead (at least not for large problems).
Without exclusion my 6-parameter runs take 1-5 hours depending on lots of variables. with exclusion everything was more than double. One reason could well be that I use small elements in excluded areas which greatly increases the element count.
I do have a 64-bit, 24GB RAM, 6-processor maching though.