What is your preference: an ND 8 or 16 filter ?

I think the gel idea is an excellent solution. There are huge choices in that area and they could be cut down to fit. Best case would be a filter ring with a slot. This would be glassless so weight would be easier to manage. May I add Infra-red filter and polarizer to the mix?
 

This filter set is a far less expensive way to go. Optically clear gel filters are very costly and a pain the fanny to cut and keep clean.