First of all, if you've hit scores in the 40s, you're done. The only reason it doesn't score higher and that the judges nitpicked is because judges are afraid to score anything too highly (i.e., a score of 50 does not actually exist) and they usually feel like they need to suggest *some* sort of improvement. I know this to be truth, or if it isn't, then tell me what *is* true. I'm a BJCP Recognized judge myself. So anyway.... scored in the 40s? Yeah -- you're done. No improvements required!
If you want to play around with the recipe, change just one thing at a time and taste it side by side with an unmodified control example. I like the Maris Otter idea. Also you could probably kick up the Munich into the 25-30% range if it doesn't turn out too dark for style. Keep the hops as they are. Yeast strains are another great idea for experimentation -- split a batch and try dozens of different yeasts if you can and taste them all side by side -- it's so easy to do. But truly, like I said, you're done. You're really just splitting hairs at this point, if it's that awesome already.