On your Dell, in Standard View, display Albums five across and scroll.
Then display three across and scroll.
Was there a noticeable difference in refresh rate?
Try a few different thumbnail display sizes to be sure no size slows the refresh rate.
MC builds thumbnails from the original Cover Art in three sizes I believe, and stores then in its Thumbnail Databases. If the display size matches one of the sizes, MC doesn't have to do any image scaling. If display size doesn't match one of the sizes it does have to do some scaling, which would be done on the server I think, although I'm not sure. It could be done on your iPad.
I would think though that if the test above showed no difference in refresh rate, then the Dell is quite capable of scaling the thumbnail image without delays. So I would look to the WiFi connection speed for the iPad, or getting a faster iPad.
If there is a noticeable difference in the refresh rate in the test, then the Dell isn't able to scale the thumbnails fast enough. I think this is unlikely though. A developer would have to say whether scaling was done on the CPU or the GPU, although you could watch the CPU and GPU loading when doing a lot of scrolling with various display sizes on the Dell to work out which is being used.
I am assuming that your actual MC Library (not the media files, but the Library) is also on the SSD, which it would be if you are using the default Library. That would be in "C:\Users\[UserID]\AppData\Roaming\J River\Media Center 25\Library".
Note that the thumbnail database is also stored on your SSD at "C:\Users\[UserID]\AppData\Roaming\J River\Media Center 25\Thumbnails". It is possible that the thumbnail database has picked up some corruption, and hence isn't indexed properly so it is slower. Shouldn't happen, but sometimes seems to. If nothing else works you could try deleting the contents of the above thumbnail directory and rebuilding thumbnails, but that is going to take a while for 50,000 files.
I don't have JRemote, but in "MO 4Media" on my Android phone scrolling with three thumbnails across is very fast, although the thumbnail image can take a moment to display so I can easily get ahead of the refresh. This is with MO 4Media connected to the HTPC MC Server as per my forum signature. JRemote may work differently to MO 4Media though, so this isn't a definitive comparison. You could download the
MO 4Media for iOS free trail version and test how fast that scrolls, as a comparison.