The .965 eyepieces are hardly ever used anymore, on the better telescopes anyway. The 1.25 is pretty standard. One differnce is apparent field. This refers to how big the circle your looking at in the eyepiece is. It's how much sky it appears you looking at if the image was projected onto the sky. The larger the apparent field, the larger the circle and the image apears larger. Now this is different from magnification. It's like a 7" TV vs a 35" TV. It's the same picture only bigger. The 68 degree apparent field eyepieces and bigger are great. 40 degree is kind of small. They are also very expensive, all makes. They run typically around $300. Are they worth it, does it make a difference? Absolutely! Not only for field size, they focus better also. I recommend the 2" draw tube with the 1.25 adapter. Some of the longer focal length eyepieces come in 2" only. Obviously, if you don't get the 2" draw tube you can never buy a 2" eyepiece or even borrow one. Many eyepieces come fitted for both 2" and 1.25. They are a little awkward in a 1.25 draw tube or diagonal. I'm not a telescope builder, but I did my research before investing $1200 in 4 eyepieces. Try to find someone who has both a 40 degree and an 84 degree around the same focal length and compair. You'll immediately see the difference. Clear skies.
That's it;
BOB SAL