I will agree that with actual tach testing, I have seen 2-300 rpm loss with those plastic deflectors. Perhaps. and I stress perhaps, you could lose less with the next size larger deflector, but good luck holding it on.
I have also seen 200 rpm by removing the internal baffle, but with proper tuning after removal, I have not seen an increase in dead sticks. It is necessary to retune after removal.
Good Luck,
Twinman