And don't even think about recording 1080p or 720p@60 without a class10 UHS1 type card
Erm no. 1080p video or 720p@60 comes out to under 3mb/second. A class 4 card can theoretically do the job. Nikon recommends a maximum class 6 for unimpeded performance on their top of the line video cards. Also my new prosumer camera supports 13 frames in the buffer and my 6 year old DSLR supported far more as well and even with a piss-poor cards of yesteryear behaved admirably when taking fast action shots at sporting events in continuous release.
The reality is that we were taking 1080p videos and shooting fast paced sporting events long before Class10 cards started coming out. Your comment is similar to those "professionals" who say that you can't photograph sports without vibration reduction, and piezoelectric focusing drives. Well I have sporting photographs from 40 years ago that prove otherwise.
Erm, yes. Sorry, but it's just math. Bitrate*compression*framesize*FPS. Raw reate at 1080p is 6.22M/s w/o compression. There is a little overhead so use 6.5 to be safe
1) Short of a very intense 60% compression you won't get down to 3M. Post processing yes, but in the camera on the fly? Pretty rare. In most cases you are looking at about 5.0M/s for 1080p. That is why many cameras have a 12minute limit on HD recording - at 12Min you've hit the 4G maximum file size. The Canon line which I am most familiar with has this limit. Many P&S cameras do as well.
2) We weren't shooting 1080p video on class 10 cards "long before they came out". There weren't even consumer grade cameras capable of shooting 1080p at usable bitrate/frame rate until a few years ago. The SD Association *specifically developed* Class 10 cards for FullHD video in alignment with the introduction of 1080p capable cameras. At the same time. Class10=FullHD=10M/s target write. That's what they are for. It's on their website: https://www.sdcard.org/developers/overview/speed_class/ I'd love to see the link wherein Nikon specifically ignores the very public, published SD standard.
That said, some premium manufactures switched to higher speed for all their manufacturing while continuing to label them seperately. SanDisk was notable for this. There are a lot of lesser labelled SanDisk that perform above their rated class speed. My advice stands: do not to try and get lucky with a class6. If you are going to shoot at 1080p@30 or 720p@60 just get the 10+UHS1 as recommended by the good folks who design them and don't waste your time.
Finally, the newer PZ lenses are just phenomenal. Stick with the old lenses if you like, but I just plain get better shots with USM +IS then I was 40 years ago on my 35m Program AE-1 without either. Stop missing opportunities and get a faster focusing lens, and we'll have to agree to get off each other's lawn!