You can't have it both ways. The more you compress the file (make it smaller), the more you lose quality. The loss may not be discernable in a 4x6 but it will be in a large print. As a matter of fact, if you want maximum quality you should convert the RAW to a tif, not a jpg, but then you will get a very big file. What I would suggest is making somewhat compressed jpgs now for small prints or web posting and - assuming you are saving your RAWs, which you should always do - when you are ready to print big make another conversion to a high quality file, make your print and then delete the large file.