For its size the FL-400 is a great little filter. Kind of a smaller version of the famed FL-1A. Unless you're going to significantly plan on extending the OCI, and doing PCs to establish condemnation points, I'd just stick with the FL400 filter. Fits easily and the beta ratios are reasonable.
The FL1A is a great upgrade, when you can get it to fit ... but most of the time, the reason the FL400 is there is because an FL1A will not fit (at least without cursing).
In a similar situation, I often recommned Toyota owners "upgrade" from the little filter to the FL400; easy swap because it's longer, but not larger in diameter. Will fit nearly all the Toyota configurations, and provides better beta ratios. Check the 51348 Wix versus the 51516 Wix and you'll see what I mean. (note: not all Toy's take the 51348; this only applies to those that do).