Adding to dmertz's answer ...
The difference between the HSA and FSA is $2900, which makes the threshold closer to 20%. But that 20% also includes Social Security and Medicare (usually 7.65%). That means if your combined Federal and State income tax is over 13%, your tax-savings will be over the 'lost' $600.
With that being said, many employer-based HSA accounts have fewer investment options than IRAs, which could possibly hinder the long-term growth.
And don't forget to factor in the added 'risk' that Plan A has a higher maximum.
