My gf was attempting to buy me the Norton set from SRD (flattening stone, 220/1k, 4k/8k) but they were sold out of the 4/8k. So I received the flattening stone, 220/1k, and a gift certificate for about $80.

The questions are: Would there be little difference felt if I substituted the 4/8k Norton with a 3/8k Naniwa? Would my Norton flattening stone be alright to lap the Naniwa? Any other suggestions?