Ben – we just released a new version 1.7 which fixes these issues with grid and which improves performance via caching. If you do install the latest version, you will see that the issue of searching a particular is solved and the users will be able to view the posts of that category irrespective of how many pages they have loaded. Pls try out the new version and let me know how it goes. I am eager to fix any problems you may encounter although I doubt you will find any with the new version.
Also, you can enable Posts Blocks widget by activating the same from Plugins->SiteOrigin widgets screen. With the new version rolled out, I don’t see a need for you to use Posts Blocks for grid function since we have pulled all the cool things we did with posts blocks into Livemesh grid widget in 1.7. They both now share the same framework.
Also, I would suggest you go with pagination instead of load more function in the new version since I find them a little more user friendly when there are large number of posts as it is in your site.