Seathal

I have 20 Custodes, 20 Sisters, 2 Contemptors, 2 Land Raiders and 2 Rhinos waiting to be converted into a "Talons of the Emperor" 40k list but also to a 30k one. I agree with you on most of these. To me, main differences: 40k is limited to a handful of units whilst 30k has more variety 40k can ally to a much wider array of lists whilst 30k is more limited 40k has amazingly powerful base stat lines and equipment all over, pretty much best "troop/basic" melee/tanky unit in the game. Shield-Captains with I5 and S6 AP2 weapons with 4 base attacks (+1 for charging and +1 for vexilla) and WS5 (with a certain LOW trait this can go up to 6) is a duelling beast and noone but the best characters in 40k will stand a single round of combat. As you mentioned T5 S2+ Fearless and Eternal Warrior with a base 5+Invul (3+ with shields) Re-rollable 1s (with CAD) is stupidly surviable even at 5x the cost of a combi weapon each. 40k vehicles are easier/cheaper to get and still provide a better transportation platform (Assault Vehicle, 5+ Invul, AV14 all around, BS5 twin-linked...) 30k has HQs ahd characters (Valdor is a beast), 40k does not (LOW has to be a "lowly" shield-captain) 30k has vets and can get more toys and specialized and customizable equipment and troops 30k has inferior transports but amazingly good grav-tanks 30k Custodians are just better at shooting and flexibility in exchange for durability and punch when assaulting, but still excell at CC 30k has amazingly awesome dreadnoughts, whilst 40k's contemptor is meant to fill the anti-AV13/14 role noone in the army can take Solution I found: Why not both? This is what I did: Build a list as heavy on infantry as you can; Custodians are amazing models all over and have great stats to make them your core both in 30k and 40k. Ally them with Sisters, it's a fluffy alliance for both 30 and 40k and can give you the boost in number of bodies and the anti-psyk power you need. Get the "Talons of the Emperor" boxset. The price of a single unit of plastic custodians is not much lower than the full box and you get a LR, a Rhino, a Contemptor, a squad of Sisters and the codexes for both SoS and ACust. This is a way of getting some anti-vehicle and transportation power for 40k list without spending too much money. Convert/Paint the transport vehicles in a way you can use them for other Imperial factions like the Sisters of Battle or the Inquisition: Barroque, Gold and Bronze, Black/Red paint scheme and Aquilas should go fantastically with any of these factions. Focus on 30k dreads and vehicles because they are much more cool. Who knows, maybe we'll end up getting full rules for FWs Legio Custodes vehicles for 40k and they look fantastic. And even if you can't use them in 40k, you'll already have a nicely converted LR for them and can Deep Strike the rest quite reliably. Depend more heavily in DR and footslog in 40k because a basic unit of Custodes is much more reliable and survivable by its own in 40k, whilst 30k Custodes rely more on specializationa and interaction with other units and transports.