The weight of a saltwater fly reel is only one factor to consider when choosing a reel. The most popular and best salt water reels are actually in the upper range in terms of weight. Look at Islander, Abel, Billy Pate, Tibor, they're all in the 6-8 oz range. Ted Juracsik who design the Tibor and Billy Pate reels designed them with durability and function in mind, that's why they have a solid cage. Reels that have a ported cage will be slightly lighter. The construction of a saltwater reel should be evaluated carefully, all the components should be saltwater safe by being anodized, made of stainless steel or sealed.
The common element in all great saltwater reels are a strong drag system. The majority of best saltwater reels (Abel, Tibor, Islander, Bauer MSL, MXP) have a draw bar cork composite drag system where the drag pressure is created by the spool being drawn in to the cage and friction on a large drag surface. The lastest rage in drag systems are carbon fiber or engineered composite material drag systems, reels such as Hatch, Nautilus CCF or NV, Ross Momentum LT and Bauer Rogue. These reels usually have a maintenance free sealed drag system which perform with consistent pressure in any condition, even underwater. The lightest saltwater reels on the market usually deploy a sealed conical drag system, which have the smallest drag surface area. Although these reels are light weight their conical drag systems have a short lifespan with strenuous saltwater use, especially with bonefish, roosterfish, albacore, tuna, etc.
You should ask yourself, what species of saltwater fish am I going to fish for? How often will this reel be used?
There's a reason why saltwater guides and professionals choose certain reels. They have been proven over time that they're dependable and will stand up to the abuse these people and fish put them through.