How many line items in the document,etc? I have about 100K+ products in my CRM system and I haven't really ever noticed any issues in reading the product and I'm on very old hardware 
.
That being said for optimal performance you need to make sure that whatever is reading that GUID is using an index on COMM_PRODUCT or setup a new index on that table. Once again this is just some basic performance tuning and I believe if you call COM_PRODUCT_GUID_GET you can provide all the index fields for COMM_PRODUCT.
Take care,
Stephen