My opinion remains that purestrain genestealers as written in 2nd Ed 40k, should remain an Arbitrator/Campaign Master tool. As relates to a Genestealer Cult gang, that would involve them most likely in the event that the cult is defending in the Storming the Barricades arbitrator scenario first released in Outlanders (and which oddly I can only find in
'tweaked' form as an LRB file in the Vault - I'll look to correct that). In short, it's a multi-gang scenario in which attackers outnumber defenders (in terms of gang rating) at a ratio of between 2:1 and 3:2. Should the defenders gang rating be on the low side, they can be permitted a balance of 'free credits' to spend on defensive measures like razorwire and wall-mounted guns. So if two gangs with combined rating 6000 attacked a Cult with Rating 2500, the Cult ought to receive 500-1500 credits for defenses, on the judgement of the Arbitrator. I'd just add 280cred purestrains to the options of a Genestealer cult.
The more complicated option would be to have immature purestrains as a recruitment option. The listed stats could then be taken as purestrain max. stats.
Reducing that stat block equally to House Ganger starting/max stat differences would then give:
M
..WS
..BS
..S
...T
....W
...I
...A
...Ld
.6
....4
....0
...5
....3
....1
...4
...2
....8 for starting
M
..WS
..BS
..S
...T
....W
...I
...A
...Ld
.6
....7
....0
...6
....4
....1
...7
...4
..10 for maximum
Wounds could not be altered down as the standard 'stealer only has one. What it does get is a whole lot of WS to soak up flesh wounds (if a player gets lucky). Though in this method, I'd give purestrain a max Wounds of 3.
That's still a very (very!) nasty starting stat block to me. Not too dissimilar to the Scaly and without recourse to weapons. But then, the scavvy combat monster has to double as their heavy weapon trooper so melee potential gets diluted, while purestrain are very
pure focussed.
My first thought would be to take another point of Strength from starting purestrains and possibly drop their Move to 4. Then I'd tailor their Advance Table to grant Skills only on 2 and 12 (maybe 2, 3, 11, 12) and limit skill choices (I'm thinking only Agility and Stealth even on 2/12), as they lack human creativity. A Move increase advance would then need to be included and a purestrain would need 14 advances (16 if starting M:4) to max out all stats (with W:3). With the standard Experience Advance Table (and I'm still running on ORB - other rulesets may vary) then, a purestrain would need to begin with no more than 50+d6 XP in order to fit all of those in.
So in fact, if you started a recruited purestrain at 60xp, it could never achieve the scary 40k stat-block even if it never picked up a skill. And then of course they are susceptible to Serious Injuries.
Hmm, I'm in danger of convincing myself here.
And I'd be tempted to ignore the M:6 altogether as with only two skill lists, Sprint is likely just a matter of time. Or start M at 6 and just ban Sprint because 18" charges on a 4'sq table is beyond rude. Ask anyone facing the Fleet rule in 3rd Ed 40k on a GW store table.
The only thing left to work out would be credit cost of recruitment. Bearing in mind that purestrains come with a 5+ armour save, ignore pinning and all psychology bar being Broken, as well as causing
fear. And any cap on numbers.
What I had been going to say before I got carried away with the above, was that the simpler option (and viable with my list-in-progress) might be to ban purestrains but hybridise the purestrain and max-human stats for the highest values of each, producing:
M
..WS
..BS
..S
...T
....W
...I
...A
...Ld
.4
....7
....6
...6
....4
....3
...7
...3
..10
I've not raised M because of Sprint, nor raised A to 4 as -with my list at least- the option to buy Extra Arm twice would actually give such a hybrid 6(!!!) attacks off a stat of A:3. Which is something I confess I had overlooked. Even starting at 0xp though, no model could reach this stat-block (24 increases from my Hybrid stats but only 20 available advances). What you'd get instead would be hybrids with varying similarities to purestrains in their capabilities.