Interesting question. It is some time since I had either to be honest, but I’d say they were two rather different wines from different parts of the Fino spectrum
The Perdido is aged for longer in the butts, so develops added complexity from almost turning into an Amontillado (IIRC) and although it is lightly filtered before bottling, I don’t think they call it En Rama
En Rama bottlings, as far as I know, are fresher styles that have some extra body because they are so lightly fined and filtered prior to bottling, but otherwise are not aged.
It rather depends on what floats your ‘barco’ really, and I am happy to make this an excuse to find some of both to try again
ADDED: What is interesting about both these wines, however, is that innovation in established drinks categories tends to happen at the borders between styles. It is hard to launch a NEW Fino, but if you innovate by making it almost-not-a-Fino then consumers start to pay attention. So En Rama made a success of the focus on freshness (the ‘natural’ trend in food and wine) and the Perdido is more about lost traditions and blending styles.
I suppose this is also (literally) true for Palo Cortado - the rule-breaker.