I love my 401A - actually Olivia's now. Somehow that kid always manages to get my better tools.
The 401A is a very smooth running machine and has plenty of power. It's also all metal inside. No plastic gears or cam stacks to fail. There are good reasons why they tend to sell for more than other models. At least they seem higher priced in my market and they get plenty of bids on Shopgoodwill. Rocketeers? All the advantages plus some very cool styling.
I don't remember the exact model numbers but there are some German made Singers from the same period that are also free arm machines.
I know you asked only about Singers but I think some of the European makers might have machines that fit what you want too.
Rodney