I'm a bit surprised that no-one has suggested that an f/2 lens is OK for many interiors, and that you should at least try it for a while, especially now that such high quality 800 films are available. Historically there has been a lot of great indoor photography with f/2 lenses (once considered 'fast') and much slower film than we have now, but no flash. Of course it all depends on the kind of pictures you want to take. Personally, I'm glad that I learned to take indoor and night-time snaps with a 50 mm f/2 lens and High Speed Ektachrome Type B (EI 160) thirty years ago.