My local yacht club has 3 Valiant 4.90s for use as safety boats. They bought the first 2 or 3 years ago and have bought the others since as they have been so pleased with them. (They still have a Searider, but the first choice of most of the drivers seems to be one of the Valiants)
They run 2 of them with 40hps, and one with a 50. Build quality is consistent acrosss all 3, and they do seem to be pretty well put together.
They handle the conditions here as well as anything of a similar size. (In a north-easterly we can get some pretty unpleasant conditions with a big swell running under a shortish chop and breaking water in the fairway.
Based on their experience I would commend the Valiant, but I have less experience of the Assault to compare. I tend to go along with the views of those who say if you want a Humber, look at the Ocean Pro or Destroyer.
If weight is an issue, the Valiant is certainly worth a look.