In general, both projects provide a solid starting point for developers working on web projects. They both get rid of a lot of tedious, some, some kind of erroneous template that many developers can recreate for each project. The details of how they go about this are slightly different, but for the most part they achieve the same results.
HTML5Boilerplate, as you noted, has been added to some build-script parts to help developers follow best practices to speed up their pages in terms of server elements such as long-future expires headers, etc. because the HTML5Reset project is more focused on semantics, content, and style. For example, HTML5Reset has a more sample structure for the content of a page in HTML5 (to show people how to use some of the new elements), while HTML5Boilerplate does not.
The parts of the response time and page speed that HTML5Boilerplate uses are becoming more and more important as more and more users are on mobile platforms, and as Google increases the effect of page response time on the page ranking . There are many documents that show a slight increase in page response time, which has a noticeable negative effect on how your site is used and perceived ( especially in eCommerce setup ... often a 100 ms slower page will receive a percentage of less sold items).
On the CSS front, most of the reset style sections for both projects are very much the same, with some slight differences in the baseline settings. However, certain IE fixes mostly coincide with the HTML5Boilerplate, which claims a bit more control than HTML5Reset over how IE styles some elements, such as form elements (e.g. checkbox / radio buttons and valid / invalid states)
The two main areas of CSS that HTML5Boilerplate covers are that HTML5Reset is not a public helper class to help make sites more accessible, such as .hidden and .visuallyhidden , as well as some significant print style adjustments that both make printing more similar in browsers. , as well as some economical and affordable things, for example, to make transparent background images (so as not to waste toner), and also add the actual URL to the links and the title for abbreviations.
I would strongly suggest reading information about all the projects and how they do things side by side, because the similarities, as well as the differences (and the arguments behind them) are very informative and helped me better decide which parts of each I wanted use.
Ultimately, like any “library” project, you, as a developer, should understand what you are doing, and probably need to customize your baseline to meet the specific needs of the project.