I thought I'd give these a punt as a temporary fix in the mk1 https://www.amazon.co.uk/Bass-Face-SPL4 ... 4+speakers
but I am very pleasantly surprised - at their general performance but also for the amount of bass they produce. Now, I do have a "high end" head unit but I think most aftermarket jobbies now pump out the same 50W per channel so the difference should be noticeable whatever you have.
I've had pretty much every brand of 6x4 in mk1s and mk2s and I have to say these are the best - especially given they are only £25. Next day delivery for Prime account holders is a bonus too.
Oh, and they come with very thick gauge speaker wire as well (although no connectors?!)