I've got a few cuts to make on some (large) offcuts of 40mm oak worktop. They are all straight, each cut up to 60cm long, from one side of the piece to the other. while this is technically within spec for my jigsaw, there's no way it's up to the job: the top of the cut may look straight but on a board this thick the back wanders all over the place, even if it take it very gently. It would also take forever even with a new blade.
So a shopping trip is in order. I'm a bit short on space, and don't want to spend a fortune on something that will be used rarely at best. I'm considering either:
a sabre (reciprocating) saw, which is compact and likely to be quite useful in the future (e.g. with a coarse tree-trimming blade). It might even replace the tired old jigsaw.
a circular saw. I haven't needed to use one in 20 years so it's likely to end up sitting in a box for quite some time. I regard it as mainly useful for wood-based sheet material, and not the thin stuff. That doesn't leave much that I actually do.
In theory I could replace/upgrade the jigsaw, but it's fine on thin sheet material and in not convinced a new one would be so much better. I'm not adverse to hiring something, if there's a much better way that's bulky or expensive.
In any case I assume I'd set up a guide fence.
So: is one of my ideas much better for the job in question (straight cuts on 40mm oak)? Which is more generally useful in the future? Or have I missed an important consideration?