Hi!
The reduction of ranges and movement rates, would have a profound impact on a lot of mechanics. One in particular I'm looking over is flyers.
If movement is reduced, the ploy of "mega-drops" of troops is lessened or eliminated, since fliers would have to loiter on the battlefield longer if the move rate is reduced and you wish to strike deep into the opponents lines. I think fliers should be the only unit to move 50cm or more in a single turn.
Titan close combat weapons would become much more useful too. Closing a 50cm gap to engage is not the same as 75 or 100 due to weapon ranges on titans. If optimal firing range is 50cm or less then CC becomes a lot more attractive.
Overall I think basic anti-personnel weapons should have a range of no more than 15cm, with most "tank weapons" being in the 35cm to 50cm range max. Few weapons should reach 75cm, with should be the direct fire range maximum.
Artillery should average between 60-75cm. Maximum should be around 80-90.
NOTHING should have ranges of 100 or more. Its just too much.
Also, as far as movement, I think going back to the AT1/SM model where charge orders gave you a bonus to you move and NOT double movement should be adopted. Also let them fire at -1 on charge OR as per one of my suggestions, where if you double move you can't fire and if you move at the lesser charge bonus rate you could fire at -1 to hit.
In any event movement rates have to be lowered. Infantry is okay at a base of 10cm, but most tanks should be between 15cm and 20cm for tracked/wheeled vehicles.
The maximum should be 25cm for grav and other "swift" vehicles. Move rates of more than 25cm are overpowered and should not exist.
Titan moves should be in relation to the size. With larger ones moving no more than 10cm, 15cm for medium and 20cm for the smallest and fastest.
I think these things make for a better game.
Primarch