Journal publication and acceptance to competitive conferences
I'll give you my own opinion, as something of an interdisciplinary scientist in a nearby field (I work in mathematical epidemiology) with publications in both places (the conference paper frankly by accident):

First, your impression is indeed correct. CS and related fields very heavily weight conference presentations and proceedings papers in ways the life sciences really don't.

In my mind, there's two things you should be considering:


The opportunity to double-dip a bit. We had a question about this recently, but I think it applies to you as well. If your project has "Life science spin-offs" and "Computational science spin-offs", you can submit to both places. For example, I have a project that will end up living in both applied math journals and clinical journals. There's no reason you can't do both.
This part is purely my opinion. When in doubt, I'd go for journal publications, for a few reasons. I've found most CS and technical people recognize that outside their field, its papers or nothing, better than the other way around. Journal papers are also more likely to get on the radar of people you want seeing your work, get indexed in PubMed (LNCS for example is not indexed in PubMed) etc. Those departments will also probably recognize your technical chops either via talking to you, the technical bent of your publications, or a few conference presentations.


I sympathize with your problem - it's sadly familiar. Generally, I'd try to figure out which audience you want to sell yourself to more, and do as they do.