As I posted on my blog, Samsung is tinkering with higher-spec'ed S5 variant definitely. The device will have Snapdragon 805, 3GB RAM, QHD(2560x1440) display and most importantly LTE Cat.6 support. Even GFXBench result surfaced online several days ago(it's deleted from GFXBench site now).
These days, I ran across some (unofficial) tidbit leaks at the Korean tech geeks community often. People there regard this new device as a matter of fact only if all the requirements are met. However, in addition to a grain of salt, you should take notice of 3 important points.
1. Even in the case the device really hit the market, it will have plastic. It's speculated that Samsung will not use metal for the device. If Samsung goes with metal, they will use magnesium as they did before, instead of aluminum. However, I don't think Samsung will set up metal processing facility for this highest-end device. The device would be very expensive and, as a result, will not be sold in big volume like S series would. Metal is not good for wireless charging, dust/water resistance, signal reception, etc. Samsung has no reason to use metal for the device just to show they can make devices with metal. It's not the matter of "they can't" but of "they don't".
2. This device is unlikely to go beyond Korean market even if it's released. Some Korean telecom companies(especially SK Telecom) will launch LTE Category 6 network sometime this year and the device is for the new network(FYI, GS5 supports LTE Cat.4). Like last year's S4 LTE-Advanced, the device will be limited to Korean market unless carriers abroad have immediate plans for LTE Cat.6 network. As far as I know, there's none. Some European carriers are testing so-called LTE-A network(LTE Cat.4) currently, thus there's huge gap between Korean carriers and the others. No carriers but Korean would require the device supporting LTE Cat.6.
3. If Snapdragon 805 doesn't get ready soon, this device will not be launched at all. Rumors say that Samsung is already negotiating with Qualcomm for 3~5 million 805 chips for their devices. Some of those can be used for this device. However, if Qualcomm fails to mass-produce the 805 SoC on time before summer, we will probably see the SoC from Samsung device in September for the first time. Yes, it would be Note 4. Even though Samsung Exynos SoCs has been better than or at least on par with Snapdragon SoCs in terms of raw computing power, Samsung is way behind regarding SoCs with built-in LTE communication function. That's why Samsung can't release this device without 805 chip.
Thus, you don't need to get disappointed with the galaxy S5 in your hand right now. The device called as Galaxy F, Galaxy S5 Prime or whatever may well be vaporware if things don't go well. It's not certain that the device would get out of the lab and see the sunlight yet. Absolutely, no need to worry. That's my 2 cents.