Good question - i'd like to hear some real-World experienced answers too. Couple of BHP improvement at most if your lucky ?? But might also make it more responsive perhaps as it would be a bit less 'choked'.............?
For what its worth - with my front CAT gone due to the Toyo manifold, i've not had a single issue with EML's, and i fully expect it to be MOT compliant [If not wanting to completely get rid of one of the CAT's; is partly your reasoning / worry ?]. ie: One seems to do the job !
******Anyway - hope thats what you meant and didn't mean something like below