No 1333MHz RAM will not hold your CPU back when clocking to 4GHz, you will need to use the 6x mem multi so your RAM will actually be slightly underclocked.
If you use 200Bclk and 20x CPU multi for 4GHz your RAM will run at 1200MHz, and if you use 191 x 21 it will run at 1146MHz.
1600MHz RAM is better, as it will run at it's rated speed when using 200x20.
But tbh, you aren't going to notice any difference in performance running your RAM at 1200MHz instead of 1333.
You might even manage to tighten up the timings with it running slightly slower, so the performance would end up being very similar anyway.