Simmering Ability vs. Pocket Rocket or...
Simmering Ability vs. Pocket Rocket or Brunton Raptor and Flex
How precise is the flame control? I'm looking to get one of these for ultralight outings this summer but was hoping to pick up one with more than just pure boiling capability if possible.
This stove simmers exceptionally well. A point that I think you've picked up on is that a stove's simmering capability is not only dependent on how well it regulates the fuel, but the flame pattern can have significant impact on how well the heat is dissipated. The SuperFly's flame pattern is one of the best and will allow you to cook as gourmet as you want while miles into the backcountry. The PocketRocket isn't the best at this because it's flame pattern is highly concentrated into a small area although the flame can be regulated fairly well.
Another stove to consider is the MSR WindPro. This is a light stove at 6.8 oz, but not quite as light as the SuperFly (4.6 oz.). It has the same burner head as the SuperFly, but has a lower profile (translation: is far more stable when using larger pots) and can be used with a windscreen. The reason is it's a satellite canister stove, not a sit-on-top type. Not only will the wind screen make the stove more efficient, it will also help to keep heat trapped in, thus making it one of the best gourmet stoves you can buy. It uses a canister and has one of the best fuel regulators (allowing for a more consistent simmer) available today.
Yet another stove would be the MSR DragonFly. It is a multi-fuel stove (can be used with diesel, white gas, unleaded gas, kerosene, etc.). It is not compatible with a IsoPro Canister however. This stove is the best at simmering of any MSR stove made! For a multi-fuel stove that is saying a lot... It isn't ultra-light (weighs in at 17 oz), but if you want one stove to work in cold weather, be indestructible, easy to maintain, great pot-supports, use of multiple fuels (less money to operate), and something you can pass down to your grandkids, this is the one!
I've used a Flex quite a bit and am pretty impressed. It doesn't burn as hot as the SuperFly or WindPro, but packs up really small. It's simmering capabilities are very good. However for the money, I would go with the SuperFly. The main reason is the SuperFly's dependability. One concern with canisters are the threads on the valve which can easily be damaged. Because the SuperFly bypasses these using it's unique clamping mechanism, you can rely on it far more than any other stove out there. It can also use multiple types of canisters (there are 40 different types of canisters in the world...the SuperFly will work on 30 of the 40). The SuperFly doesn't pack as small, but it's larger burner head will give better cooking results based on my own personal experience.
The Raptor is ok, but it suffers from poor wind resistance. It's simmering isn't that great due to the design of the burner head, but the price is good. I guess you get what you pay for... It isn't a bad value when you consider it comes with a piezo ignition, but I tend to steer away from stoves that have this. The reason is they will inevitably fail and then you're left with a stove that doesn't work properly.