IIRC, faster loading is planned for 2.0 (at least for library filters which are a majority for most users).
Reduced preview size ... yes, I understand what you're talking about. It's a feature, but might be annoying, I see. It's very quick to change actually -- so after saving it will stay at full resolution, so ask Vlad if he would like to change this
Try turning off "Reduce preview size for large images" checkbox in Tools->Options...->Rendering, this will get rid of automatic image downsizing for preview purposes.