its true that the intake will slow it down, but it will kill the flow quiet a bit as well. Ive tested heads at 298cfm and after putting a victor on ...they flowed 265-270's cfm. before working the manifold it can eat up 30 something cfm.
The rpm and ld340 intake for instance only flowed in the 220'scfm per runner as cast.
You may find yourself in that case with only about 215-220cfm after the intake gos on.
How about skipping on the sand rolls and leaving the port rough, also...sometimes a basic 3 angle is all you need, in other words too many angles can work against you in the fps depot.