The display rate shouldn't affect the acquisition rate, so having a bigger screen shouldn't mean a reduction of captures from, for instance, 40k/s to 10k/s. Which was the point.
Oops. I missed the point, as usual. Sorry

I can understand the reduction of captures if each capture sequence is at most as long as is shown on the screen, but otherwise I'd expect the captured signal (and the acquisition buffer) be wider than the screen.
That leads to an interesting question: Should an USB scope always provide the sample sequences, or would it be better if it sometimes returned the combined acquisition buffer instead?
There are many forms such a buffer could take, but the simplest form I can think of has 256 8-bit bins per time unit, forming a 256-bin histogram of the acquired curves at that point in time relative to the trigger. The computer could request updates only on a specific section (a screenful), and when paused, request the entire buffer (up to whatever time depth is available), or the data from the latest acquisition. (That assumes an 8-bit ADC, by the way. For an N-bit ADC, I'd expect 2
N samples per time unit.)
Typical data rate could be for example 1920 time units 25 times each second, i.e. 12,288,000 bytes per second.
More generally, given
W time units,
F times per second,
N-bit ADC, we have W×F×2
N bytes per second at 8-bit bins (up to 255×F acquisitions per second), and 2×W×F×2
N bytes per second for 16-bit bins (up to 65535×F acquisitions per second).
While one might think that this contains the
display information, it is actually just the histogram of the acquisitions; i.e. full information (except order of acquisitions), time-wise limited to
W time units relative to trigger point. It's also quite feasible to implement on any hardware that has the memory bandwidth to store both the latest acquisition and access one entry of the 2
N-byte or -word histogram for that time point. Maximum sample depth or
W does not affect the work needed to be done, assuming double buffering, except for the zeroing of the memory after it has been sent (to prepare for it to be useable as the histogram buffer).