Let me take a shot at this.
HP: I think our latest Frankenstein monster should have decent HP. Good, but not enough for 101 HP subs. Substitute/Sunny Day/Solarbeam/Fire Blast would rock anything, as would its Physical counterpart (as well as being able to drop Blissey in a moment's notice). Since the seeming success of this Pokemon seems, even in this early stage, almost entirely hinges on whether or not he can get off a Sunny Day, I'd say 90 HP would be reasonably high.
Attack: Let's face facts: there aren't really that many usable Fire physical attackers. If the idea of this project is to diversify the game and shake up the threat list as it is, I say we give this guy some muscle. 110 Attack is my call.
Defense: As stated before, this guy should be able to take a hit. However, he shouldn't be able to take too many hits. His typing is already a total Special sponge, so I say we balance that with a moderate Defense. 90 Defense seems okay in my book, and will keep his build Balanced with Attack.
Special Attack: I am terrified of this guy being the ultimate Sunnybeamer. I do not want that, Sam I Am, as making this guy heavy on the Special side will essentially obsolete all other Sunnybeamers. He shouldn't play the functionary roll of a Heatran/Mojonbo love child. We want him to stand out from the crowd. As such, I'll call for 70 Special Attack.
Special Defense: Again, I want this Pokemon to stand out. He shouldn't be ultra bulky if we declared him Balanced, and his typing is, again, a total Special sponge. I would say 75 Special Defense.
Speed: We want this guy to stand out from the crowd, right? Well, if we don't want him to be a lackluster Bulky Infernape, I say we give him exactly 66 Speed - just enough to outspeed Infernape after a Sunny Day, but still outsped by everything that outspeeds Infernape. Since Infernape has fallen to the role of a Special/Mixed attacker, this guy could be what Infernape always dreamed he could have been. Also, having exactly one point of speed over a Max+ Infernape is awesome, isn't it? Balance is key here, because one more point of Speed and a Max Whatevermon will tie with a Max+ Gengar, since Gengar is one of the few 110+ crowd that can actually pack a STAB that this fellow is weak to. Of course, I don't want Gengar, and already massive threat to nearly everything, to be a hard counter - which is why our new Pokemon SHOULD be able to possibly outspeed any non-scarfed variety. However, it should come at a cost (namely wasting your nature on a pretty lackluster stat as compared to that gorgeous Attack or relatively high Defense, and pumping 196 EVs into speed anyways), which will obviously be something that would come into consideration during testing.
90/110/90/70/75/66 lands us exactly at 501. Not exorbitantly high, but if we try to push him any further in any areas, we'll either break him in one sense (such as the very precise speed) or another (the style and build we voted for). We likely could boost his defenses a wee bit, but you have to ask: would making him rock solid really benefit the metagame? Revenankh is already experiencing a state of semi-broken play, and while you could just chalk it up to there not being enough data and that people don't know how to counter it correctly, the main problem is that it's obviously very easy for him to set up. I know that a good Speed boost isn't the same as +2 Attack/Defense, but we just have to be cautious with the ground we're treading here. Ask yourself: how many Pokemon can reach 110 Attack/Speed and still have moderate defenses? Now ask yourself, would it be good for the game if they all had good defenses?
So, to answer the poll, I guess I'll just sum up my thoughts here.
We don't want the ultimate Sunnybeamer here, so
Attack: Physical
We don't want him to be able to switch in with impunity on pretty much any special user this side of Azelf, so
Defense: Physical
And lastly, we don't want him to be monstrously fast after that Sunny Day, but fast enough to reach a very specific speed which lies cozy between Infernape and Gengar, so
Speed: Medium (66)