Suggestions HP FB 500 or 700

Have you checked out the EFI 16H. We love ours and the white is very opaque.

 

I would caution against the FB series if the expectation is opaque white. Also banding and registration was an issue on clear substrates when I had one. Have someone run a file that you setup for white and take a look for yourself before making a purchase. Probably not what you want to hear because you can get one fairly inexpensively these days, but we had a lot of issues with white and double sided prints. For my money, I'd look at an EFI or possibly Vanguard, and if you could foot the lease, take a close look at the R-Series from HP, but you probably won't find those used yet since they are new to the market.