Interesting...but, what gives me pause is 'over cooking' the PC. Various brands and blends of the poly I'm sure react to 'over cureing' differently.
For me, using clear gloss & before I had a reliable thermometer...
...I found that my oven was hitting 475*F., & running @ 15 minutes, it turned the clear to a shade of light grey and it would not pass the hammer test. Soooo...I'm a bit leary of trying to PC and H2O drop at the same time.
In fact, I don't water drop anymore at all since I've collected enough various Pb's to mix what I want from the start. I've also found out that PC'd casts can be pushed harder than you might imagine possible, so my quest for hardness has relaxed somewhat.
The thing about success with H2O dropping is having enough Sb and/or As to effectively increase by a greater degree of BHN's. If your Pb is Sb poor it'll do not so well...if it's rich in Sb it'll get harder, kinda relative to that and we all seem to have different blends of Pb so the whole thing is a dice-shoot.
I've wondered before if shortened oven times might just harden just the outside of the cast instead of all the way through...I dunnoh, all I know is that I don't scrape Pb out of barrels anymore so the way I see it is..."I win!"
You casts your Pb & you drop in water & and you get what you get...besides that...we generally put too much emphasis on BHN instead of blend.
But one thing is for sure...I sure don't have any problems with all of us 'tight-wads' experimenting and doing just whatever the heck makes us grin!