that gravel frame does look interesting, just as a regular gravel frame. IMO that 50c tire clearance would be a bit overkill for the terrain you are describing. Could be good if you want to get into more gravel though.
I'm not as familiar with all the frames out there as a lot of other people on this forum but I would be surprised if there is not a good middle-ground option that can fit 38-42c in the same price range.
Road bikes are usually designed to have you positioned a little more forward and get your weight further over the front wheel (helps with stability/prevents speed wobbles, especially if you have deep rims). Gravel bikes are often designed to have your weight further back to keep traction over the rear wheel so it does not slip on loose terrain. They're usually longer with the intention that you will run a shorter stem (this can feel "nice and responsive" to some and "annoyingly twitchy" to others). To me, the concern about riding road on a gravel bike, would be more about handling than speed. It might handle a bit weird and throw off your sense of balance.
From the geometry, I can get a vague idea of how the new VB gravel bike would handle on road. It has a similar seattube angle to most road bikes and a zero setback seatpost so it does not actually position you further back like many gravel bikes do. It does have a kinda long top tube so you might need to size down and use more spacers under the stem or use a shorter stem and have that twitchier steering. It also has a slack headtube angle which will position the front wheel further out from under your weight, probably making it feel a little less stable in front. If you're planning on bombing technical descents it might not be the best, but for casual riding its probably fine. In reality, many of these technicalities are small enough that most people would not notice them.
