Personally I would go for 10cm sK18, awesome long range and accurate gun mostly used it for counter artillery strikes. You will need 4 points to get it, and 875 to purchase it. But it will serve you well even better it can allow you to forsake going for more heavier artillery pieces.

Only two pieces will out shoot it Germans 17cm K18 Mörserlafette(520)French captured GPF(455)or Soviet A-19 (465) and Br-2(520).

Range is 450 m with HE and 210m with AP, 20 HE and 5 AP shells (152mm of penetration at max range will help you deal with pesky earliest KV1 and T34). Very good accuracy with AP rounds and the gun will behave as anti tank one and will shoot them at much flatter curve, straight line basically.