I knowthis is probably something that you already have in mind but, have you made sure that the images in your email are as small as they could possibly be without being pixelated? Are you sure that you don't have an excessive amount of code in your build which makes the processing time slower for different clients (we ran into this problem and had to clear up some of the code and that solved it)?
Usually the ESP has a link shortening method or code you can use, if you are using Salesforce marketing cloud then it would be something like this in the code. 'WrapLongURL("http://example.com/exceedinglylongimageurl.jpg")' but it only workls if the url is 975 character or longer on the receiving end user.
Here's a quick hint that i got from Litmus. Hope it helps! You basically use the exact mesurements of the device and set the targeting that way.
I'm looking to do this myself, the answer closest to a 'yes' that i've seen in being able to target specific devices with very narrow media queries that only work for that one device on that specific ration. Theoretically, this should work like a charm but does involve a bit more grunt work than usual and I'm still doing deeper research on it. If I may ask, what platform are you using (Mailchimp, Litmus, ExactTarget)?