I got a Minim 300 in one of the sales I think in '10, and I used it last Sept '11 in warmer temps and was very happy with it. Compact, light, warm.
However, this September's weather has been colder and I was in some valleys in the last weekend when temps got the ground to frost (so just above freezing?) and I woke cold in the night. Of course when trying to sleep and get comfy you have some time to ponder the problem, for me the Minim 300 is too narrow in the shoulder-hip area for handling about-freezing, I had to sleep on my back to stay warm enough, there was enough room for baselayer type insulation but no way could I add a down jacket type insulation, its simply not wide enough. If I turned onto my side and pulled my knees up, my back became cold, presumably due to down compression. if I'd had some baselayer leggings with me, would have made a difference.
So overall, for my body size, Minim 300 only was its stated warmth lying on my back straight.
I had a further problem, not specific to PHD Minim 300 but to Drishell and to my tent, I had used a Laser Comp, not the Tarptent Notch I own, and the LC struggles to get air circulation, the inside of the tent was wet and any touching of the inner got the Drishell wet, and indeed I was woke 4am by dripping of condensation in my face. No rain.. The Drishell was not holding this all back, it was getting the down inside wet, suffiient after multiple nights transmitting a bit of the black dye from the inner to the gold outer.
I was keeping on top of down dampness via the sunny mornings after the still cold nights drying my bag, meaning I was not hiking til about 2 hours later to wait for the sunshine to hit the bag and then dry it. In certain combinations like wet morning after still night, I'd be packing a wet bag.
I don't have the solution, just know some combinations are almost failing.
On the plus side, I did from Lakes get to see Snowdon, then IsleOman, then Northern Island, then Scotland via a loop around and in the evening some SneckLifter, and then the Milky Way with the lack of light pollution. Which is what it is all about.