Hi alpydawg. Welcome to the Zone! It's about TIME you posted. I also have a Grizz SX3.
I'm pretty sure that the Sx3 and X3 have the same spindle bearings. The problem is not really with the bearings, but the inferior Chinese grease that they are packed with. I recommend that you disassemble, clean and repack the bearings. Or, you could as easily REPLACE them and repack.
Here's a PDF with bearing disassembly details:
Can we please have some details (and maybe some pics?) of your speed improvement mod?