it's like 4K TV, it's useless for anything less than 50'' you cant tell any difference, a large res is for a large screen, so 4K is best for over 60''...... 1080p is best for 50''
This isn't true, people can tell the difference between 1080P and 4K on a 42" TV. Some people might not be able to, but that doesn't mean you should make such an absolute statement.
OLED ?......that's still 1080p, but the better the contrast ratio the sharper/ more 3D the image will look, so OLED (that has a truly massive contrast ratio and colours that you've never seen before) will look sharper than 4K
OLED isn't "1080p", they have simply made 1080P OLED displays because it's currently the "standard". Also contrast ratio doesn't make an image sharper or "more 3D". If the display is truly 3D then the stereo imaging will determine how "3D" the image is, contrast ratio determines contrast, not sharpness. The contrast on a TV can and does influence image quality a lot, but it's not part of the sharpness. Sharpness in its most basic terms is dictated by the overall resolution of a display.
What you probably mean is that a 1080P OLED TV will look overall "better" than an LCD 4K display simply because most people are more likely to prefer the increased contrast and colour vibrancy over the increased resolution and sharpness from a 4K LCD.
For example, I have a Galaxy Note 2 phone, and I think the display on it is great. The contrast is great, the colour vibrancy is great too, but it's definitely not the shaprest of displays.
The iPhone 5 and Nexus 4 for example, have sharper displays simply because they've got more tightly packed together pixels, however I'd sooner take the black levels/contrast and colour vibrancy of the OLED display over a sharper LCD display because I prefer those factors to straight up sharpness, that doesn't mean that I wouldn't prefer the OLED display on my Galaxy Note 2 to be higher resolution (sharper).