24V input would certainly help reduce input current and hence increase driver efficiency and thus drop waste heat losses.
Hyperboost does have an EXCELLENT thermal path from the components that generate heat losses to the back side of the PCB. Mounting the PCB via the supplied thermal pad or high quality double side adhesive thermal tape will provide a very good path for the components to transfer the heat to the heatsink.
The key is you have 5 to 6W of heat you need to radiate/convect etc - so you need to determine whether your enclosure and heatsink can dissipate that heat while maintaining a stable temperature to the PCB.
From my own measurements, the supplied thermal pad material easily will keep the 'hot' components within about 10C of the heatsink. So, if your box/heatsink runs at say 50C stable, then the hottest a component on hyperboost will reach is 60C. Given all the 'hot' components have excellent thermal paths from the junctions to the PCB (all have thermal pads) you will have a very conservatively running driver configuration.
So, YOUR job is to see what temp your case (that hyperboost is mounted to) stabilizes at when running long term. 60C is what I call the ouch test - you can touch 60C for a while, but after a bit you'll go ouch and want to remove your finger. So, if you can touch the outside of the box where hyperboost is mounted on the other side and keep your finger there, then I'd say you have a safe operating temperature - ASSUMING you have hyperboost firmly mounted with the thermal pad/tape material to the box and the box is made of aluminium etc...
Oh, also, the 5A max input current is a conservative figure, so running it at 5A long term is not a problem IF the heat dissipation issues are addressed.
cheers,
george.